There are something fishy with exchanges i've used. I remember putting a buy order for a coin at a price of 11 sats and no one had any orders up, hence i was in the front of the queue. Weeks later i checked that some of my orders were matched and looked at the trade history and saw more coins matched at 11 than what i got matched. If i was in the front of the queue then my partial matched orders would match the trading history.

I got the feeling that exchange operators can jump themselves in front of the queue if they wanted to.