There are players of different levels buying and you can't buy a 6 star player in Auction. So sometimes you have more chance of selling a X9Q or X4Q 4* player (for example) to players a level below.....as they will see it as a 5* player thats very close to being a 6*.

I hope I explained that right. It made sense when it left my brain but took the long way to my fingers. If not someone else will help.