I notice Interactive Broker market data is different than my other broker. Especially bid / ask values.
In addition to what the other posters said, there maybe two additional possibilities:I have noticed many times that when I enter a limit order to sell options on the bid, the bid suddenly moves lower and I don't get filled. I have noticed this even with 1 lots while there were where hundreds of contracts sitting on the bid and all of a sudden, as soon as I place my sell limit order at the bid price, they all vanish and move lower. I have never sold options using a market order, but if I did, would that still happen? I don't think it should because other traders should not be able to see market orders, only limit orders. I reason that market orders should only be visible by my broker and the exchange would execute them on first-come first-serve basis against best limit order offers on the books. Is that true?
In addition to what the other posters said, there maybe two additional possibilities:
1. A rapid changes in the underlying will instantly change the bid/ask and your offer may just be coincidental.
2. If your option is thinly traded, often the bid and ask sizes are very limited so if your lot exceeds the bid lot, it won't get fill. Just this morning I only got a fill after I reduced my lot size. Right after that, the bid ask changed. Since the underlying price did not change I assumed I moved the market.