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Why is there so much variability on interest rate accounts
Pay attention to nickel-and-dime charges (atm fees, low balance fees, limit on atm transactions per month, charge for human teller transaction, charge for paper statements or tax records).  Consider that a financial company will spend on the order of $100-500 to sign up a good customer.  Are you getting this in a cash bonus, competitive high interest rate, reasonable other gift, or advertising directed at your eyeballs?  A variation in rates less than 1% easily fits into a marketing cost and there doesn't have to be any other magic to it.