I wish there were an easy way to look up which charity shops in my area have a copy of a particular book and how much it costs. A lot of them already keep track of who donated each book to them if the donor has made the appropriate declaration for gift aid so they are already tracking individual books. All it needs is a bit of organisation, perhaps, to put all the data in one place.

I don't think they'd have a reason not to use such a system if it existed. In a few cases they might be forced to lower prices or fail to sell a particular book but I would guess it would be a net gain for everyone.