At shows at least by me (North Jersey) dealers are there to deal.. meaning they usually price a bit hi expecting to negotiate. I usually ask if they have room then offer about 25% off what their price is , especially if multiple books. All they can do is say no, but most just counter somewhere in between and I go from there. Good example- at a recent show I picked up a decent copy of Forever People 1- it was marked $110 - I asked if he had room.. he immediately said he could do $90 - I now knew he was motivated to sell, so I said I could do $75 he thought for a second and accepted. That was 32% below marked. I probably would have went a bit higher but he showed his cards with initial reaction.