A guy named Jack Canfield taught to "Ask, Ask, Ask' The worst outcome is a NO but in many cases they will accomodate you. I do it @ hotels for free upgraded rooms, upgraded seating on long flights and recently at a LGS when they did not carry the grade of ammo I wanted but would accept (for a price) an internet shipment of that type ammo.
When the shipment came in I asked for a military discount on the processing cost...'NO, the boss is a Marine'. (What that had do do with anything I am not sure and did not ask.)

'How about cash vs CC'....YES! Had I not asked I would have paid a higher processing cost.
When I was selling, on consignment, through another LGS, we agreed on an asking price and a lowest acceptable offer. Like another poster said, used guns can be dickered over. Believe it or not......all firearms sold at the original asking price.....no one tried to negotiate. Sad for them

but good for me.

Which reminds me I hope everyone asks for a better price on a new (and used) automobile. Their mark-up includes room to negotiate.
OK, OK...I am off my soap box.