The thing with shop prices is also that consumers have rights, even on second hand gear, and can bring stuff back and complain. I would feel safer buying from a shop I can take a faulty item back to than buying from a private individual on eBay or wherever, that has value in the pricing too.
But generally at the moment prices to sell gear at are terrible. It is difficult to shift stuff without taking a hit and has been for quite some time. Also, you get the idiots who expect something for nothing, making offers at way, way under the asking price or buying something to only complain. I had the misfortune of two of these cretins at the same time on eBay, one trying to claim that a screw missing off the battery compartment of a pedal was a massive, massive issue, and the other trying to claim that the speaker of an amp had been disconnected through rough handling and improper packing. Both were just trying to screw a load of their money back from me. Not worth the aggro.