Offer your insights or judgment on the input financial query or topic using your financial expertise. Reply as normal question answering

Purchasing options between the bid and ask prices, or even at the bid price or below?
This sometimes happens to me. It depends on how liquid the option is. Normally what I see happening is that the order book mutates itself around my order. I interpret this to mean that the order book is primarily market makers. They see a retail investor (me) come in and, since they don't have any interest in this illiquid option, they back off. Some other retail investor (or whatever) steps in with a market order, and we get matched up. I get a fill because I become the market maker for a brief while. On highly liquid options, buy limits at the bid tend to get swallowed because the market makers are working the spread. With very small orders (a contract or two) on very liquid options, I've had luck getting quick fills in the middle of the spread, which I attribute to MM's rebalancing their holdings on the cheap, although sometimes I like to think there's some other anal-retentive like me out there that hates to see such a lopsided book. :) I haven't noticed any particular tendency for this to happen more with puts or calls, or with buy vs sell transactions. For a while I had a suspicion that this was happening with strikes where IV didn't match IV of other strikes, but I never cared enough to chase it down as it was a minor part of my overall P/L.