It could be the proprieters of the stores. Or (more likely) it could be affiliates. There's a pretty good supply of affiliates that are willing to spend more than they make. They will give up after a while, but, like I said, there's a good and seemingly endless supply of the gullible.
The Adsense may or may not have anything to do with arbitrage. If these are "free" small business stores, they need to get revenue from somewhere, and thus the Adsense.
Not a great deal for the store proprieters - I'd certainly avoid something like this. Who wants a store where you have to scroll down past ads to get to the store?