I think if it is Buy it Now you have a right to be suspicious, but if it is an auction then I think the sellers take the risk that they may actually lose money on the auction. I think their business model is that you win some you lose some, but if you average out in the black then that's OK.

I've been using an ebay seller for about a year who lists HCs for 7 dollars. Sometimes they sell at list price, other times they go substantially higher, usually only to 14 though. I would hate to think that he is stealing them. In fact, he told me that a supplier brings them to him. The new ones are obviously shrink wrapped, but sometimes he has older books which are also wrapped, but obviously not the factory wrapping.