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What do you call that?
The difference is that a scalper extracted $2.50 out of the economy for doing nothing of value at all.
I remember the original eBay banner ads. They went something like "The thing you want in Washington, is sitting on a shelf in Ohio. Who knew?" He is doing exactly what eBay started out doing. The local area might not care about the book, but someone does. And there is value in it.
One year I decided to get a music keyboard on sale at Target for my kids for Christmas. The two Target locations near me were sold out. One in a poorer area had a ton in stock. Each market is different. Don't assume that the books in one area will always appeal to the locals. I have sold books on Half.com for much more than I paid at the local resale shop after it was marked down several times, and I didn't even have a scanner. Just a hunch.