How do credit card payments work? What ensures the retailer charges the right amount?
When you give your credit card number and authorize a merchant to charge your credit card, the merchant then gives the information to their merchant processor which in turns bills the bank that issued the card (it's a little more complex and it all happens instantly unless the merchant is using the very old fasion imprinting gizmos). It is possible for a merchant to attempt to charge you more than you authorized but if they do they risk a fine ($25-$50 for a chargeback) from their processor, the legitimate portion of the charge as well as increasing the processing fees charged by their processor or even the possibility of loosing their merchant account entirely and being permanently blacklisted by Visa/Mastercard. In short no legitimate business is going to intentionally over charge your credit card.  There really isn't significant risk in using a reputable online retailer's order forms. There is the possibility that their database could be compromised but that risk is lower than the risk of having an employee steal your credit number when you give it to them in person. Besides in the US at least the most you can legally be held liable for is $50 assuming you notice the discrepancy within 60 days of statement the charge appears on and most banks limit liability to $0.  Over the years I have had a number of different credit card numbers stolen and used fraudulently and I have never had to pay any fraudulent charges. "Your credit card limit is nothing more than a simple number.  When you purchase something, the merchant receives a number (i.e. the amount of the transaction) from your card company (e.g. Visa) in their bank account, and that number is subtracted from your limit (added to your balance). The amount is recorded, and isn't changed, so that's how they get the ""exact"" amount you paid.  Transferring a number is easier than the retailer having to wait for cash to get from you to your card company to them.  Moving numbers around is the basis of the modern financial system. And yes, it is always a risk to let someone else have your credit card number.  An untrustworthy company/person may use it to charge you without your permission, or if they have your full details they could use it as if they were you.  With a reputable retailer like Amazon, the main risk is data theft: If a security hole is found in Amazon's system, someone could steal your credit card info and misuse it."
"I strongly suggest you look at CreditKarma and see how each aspect of what you are doing impacts your score. Here's my take - There's an anti-credit approach that many have which, to me, is over the top. ""Zero cards, zero credit"" feels to me like one step shy of ""off the grid."" It's so far to the right that it actually is more of an effort than just playing the game a bit. You are depositing to the card frequently to do what you are doing. That takes time and effort. Why not just pay the bill in full each month, and just track purchases so you move the cash to the account in advance, whether that's physical or on paper?  In your case, it's the same as charging one item every few months to keep the card active. If that's what you'd like to do, that's fine. I'd just avoid having the card take up too much of your time and thought.  (Disclaimer - I've used and written about Credit Karma. I have no business relationship with them, my articles are to help readers, and not paid placement.) mhoran's response is in line with my thinking. His advice to use the card to build your score is what the zero-credit folk criticize as ""a great debt score."" Nonsense. If you use debt wisely, you'll never pay interest (except for a mortgage, perhaps) and you may gain rewards with no cost to you." "Ditto Nate Eldredge in many ways, but let me add some other thoughts. BTW there are not four types of account, but five. You're forgetting equity, also called capital. Would it be possible to design an accounting system that does not have 5 types of accounts, maybe is simpler in other ways, and is internally consistent and logical? I'm sure it is. But what's the advantage?  As Nate points out, the existing system has been in use for hundreds of years. Lots of people know how it works and understand it.  I'd add: People have long since worked out how to deal with all the common situations and 99% of the odd cases you're likely to hit. If you invent your own system, you're starting from scratch. You'd have to come up with conventions to handle all sorts of situations. How do I record buying a consumable with cash? How do I record buying a capital asset with credit? How do I record paying off debts? How do I record depreciation? Etc etc. If you worked at it long and hard enough and you're a reasonably bright guy, maybe you could come up with solutions to all the problems. But why?  If you were approaching this saying, ""I see these flaws in the way accounting is done today. I have an idea for a new, better way to do accounting"", I'd say good luck, you have a lot of work ahead of you working out all the details to make a fully functioning system, and then persuading others to use it, but if you really do have a better idea, maybe you can revolutionize the world of accounting. But, ""The present system is too much trouble and I don't want to bother to learn it"" ... I think that's a mistake. The work involved in inventing your own system is going to end up being way more than what it would take to learn the existing system. As to, Aren't liabilities a lot like assets? Well, in a sense I suppose. A credit card is like a checking account in that you can use it to pay for things. But they're very different, too. From an accounting point of view, with a checking account you buy something and then the money is gone, so there's one transaction: reduce cash and increase office supplies or whatever. But with a credit card there has to be a second transaction, when you pay off the charge: So, step 1, increase debt and increase office supplies; step 2, decrease debt and decrease cash. Credit cards charge interest, well you don't pay interest to use your own cash. Etc. One of the beauties of double-entry book-keeping is that every transaction involves a debit and a credit of equal amounts (or a set of debits and credits where the total of the debits equals the total of the credits). If you combine assets and liabilities into, whatever you call it, ""balance accounts"" say, then some transactions would involve a matching debit and credit while others would involve a positive debit and a matching negative debit and no credit. I'm sure you could make such a system work, but one of the neat built-in protections against error is lost. There's a very logical distinction between things that you have or that others owe you, and things that you owe to others. It makes a lot of sense to want to list them separately and manage them separately. I think you'd pretty quickly find yourself saying, ""well, we have two types of balance accounts, those that represent things we have and which normally have positive balances, which we list on chart A, and those that represent things we owe and which normally have negative balances, which we list on chart B"". And before you know it you've just reinvented assets and liabilities." "I too am a full-monthly-statement-balance payer and I received a balance transfer offer from my credit-card company. This one was quite different from many others that I have read about on this forum. I could do a balance transfer for any amount up to $X from another credit card, or use the enclosed ""checks"" to pay  some other (non-credit-card) bills, and I would not have to pay any interest for 12 months on the amount thus borrowed.  But, There would be a 2% service charge on the amount I was borrowing. This amount would be billed on the next monthly statement, and it would have to be paid in full by the due date of that month's payment, that is, within the 25-day grace period allowed for payment of monthly statements. Else, interest would start being charged on the unpaid part of the service charge at the usual humongous rate of H% per month. If I had not paid the previous month's balance in full, I would be charged interest at H% per month on the service charge starting from Day One; no free ride till the due date of the next month's statement. Of course, the balance carried over from last month would also be charged interest at H%. If I had paid last month's bill in full, but there were any other charges (purchases) during the current month, then  unless the entire amount due, this month's purchases plus service charge and that ""interest-free-for-twelve-months loan""  balance was paid off within the 25-day grace period, my purchases would be deemed unpaid and would start being charged interest. In short, the only way to avoid paying interest on the amount borrowed was to start with a card showing a $0 balance due on the previous month's statement, not make any charges on that card for a whole year, and pay off that 2% service charge within the grace period. It might also have required that one-twelfth of that interest-free loan be repaid each month, but  I had stopped reading the offer at this point and filed it in the round circular file. In short, while @JoeTaxpayer's tale of how ""As a pay-in-full user, I've used the zero rate to throw $20K at the 5.25% mortgage"" is undoubtedly how things worked once, it is not at all clear that they still work that way. At least, they don't work that way for me.  Heck, once upon a time, for a period of about 3 months, you could earn 1.5% interest per month from the credit card company by overpaying your credit card bill considerably. Their computers then just ""added on"" 1.5% interest by multiplying your credit balance -$X by 1.015 and so you got 1.5% per month interest from the credit card company. The credit card agreements (and the software!) got changed in a hurry, and nowdays all credit-card agreements state in the fine print that if you overpay your bill, you don't earn any interest on the overpayment." The answer is the next sentence from the Wikipedia article: The precise manner in which interest is charged is usually detailed in a cardholder agreement which may be summarized on the back of the monthly statement.  Your previous question on credit card interest rates quotes the sentence after this. You have to review what the agreement for your card says. Also keep in mind the bank wants to make money from you. The more interest and fees they collect, they better they like you. If enough card holders adjust their behavior, to minimize interest and fees; the bank will then adjust the credit card agreement to get money a different way.  Yes, you are right it would seem fair to only charge interest on the smaller amount, but that doesn't allow the credit card issuer to maximize profits. I would presume this goes entirely through the credit card network rather than the banking network. I am guessing that it's essentially the same operation as if you had returned something purchased on a card to the store for credit, but I'm not sure whether it really looks like a vendor credit to the network or if it is marked as a different type of transaction. It depends on your bank and your terms of service, but using the card one way or the other may affect things such as how long it takes to process, what buyer protections you have, etc.  It also affects the store as I believe they are charged differently for debit vs credit transactions. They charge merchants a transaction fee, typically between 1% and 3%, for processing every credit card transaction. And of course they make money on interest charged to customers even if they pay on time, as long as the customers don't pay off their balance in full every month. Most merchants (also in Europe) are reasonable, and typically are willing to work with you. credit card companies ask if you tried to work with the merchant first, so although they do not enforce it, it should be the first try. I recommend to give it a try and contact them first. If it doesn't work, you can always go to the credit card company and have the charge reversed. None of this has any effect on your credit score (except if you do nothing and then don't pay your credit card bill). For the future: when a transaction supposedly 'doesn't go through', have them write this on the receipt and give it to you. Only then pay cash. I am travelling 100+ days a year in Europe, using my US credit cards all the time, and there were never any issues - this is not a common problem.