The store owner does sell cards for some of the patrons, like myself. Me personally, I appreciate this since it can be a headache and it helps fund future purchases. Plus why would he not have a vested interest in how much it goes for? If it goes for higher, then he gets to move more product. I can't tell you how many times he's had to talk me out of listing a card auction style over putting it on Buy it Now. I always want to go for auctions and he talks me out of it, and it's worked out in my favor every time.
In the end, how does this make me a sucker? It just works better for me and it's a service that I appreciate.