It happens on occasion that stocks are sold at BID by a market maker. On occasion a market maker may buy back shares at Ask. These things do happen and they cloud what is really happening with a stock. There is one stock I buy almost every week and many times I have been sold stock at Bid. There are reasons why this happens but like the old long joke about the monk searching for the meaning of life, you have to be a market maker to know.
Market Data 
Markets 
AI
