On ABE and Bibliofind, by the way, there is no prioritization. It's a free market and the nicest copy at the fairest price is the one that sells. Looking to the future, the more books Alibris amasses in it's warehouses, the less chance its sellers who maintain off-site stocks will have of selling anything. The more books they amass, the less they'll even need outside sellers. To summarize, Alibris takes their sellers' books and markets them as their own.
Sellers come away with nothing but money.
They have no idea where that money comes from, how to increase or decrease the flow, or how long it's going to last. The name of the buyer is the only true prize in this game and Alibris is the one who gets it. It's worth far more over time than the price of any book that any seller sells to any buyer. Alibris does not take kindly to criticism, by the way. The great magic of the internet is that it brings people together.