buying:
--smartphone
--list of things you want/need with "OK price" and "must buy price" (example, .45acp ball ammo in brass case - OK price 40cents/rd - must buy at 25c/r)
this list should fit on a 3x5" card, hardware on front, ammo on back - that's all the Mrs and I can keep track of between us, at least
--small flashlight (a single "AAA" light is good)
--backpack if making heavy purchases
--rifle-size gun sock if there is any chance of buying a rifle
--cash, and be ready to make change (don't just take $20 or $50 bills)
sleazy tip, distribute your cash or leave half with the Mrs, so you can always haggle based on the "well I can do $___ right now"
--if someone isn't interested in a trade, drop the subject
selling:
--for the love of little children and the benevolent FSM, have your sale goods MARKED with a clear model, chambering, and price ... visible from 10 paces if you're walking around trying to sell them, visible from a height of 7' if you're leaving them on a table for sale
example:
STEVENS MODEL 24 COMBINATION GUN
.22lr & 20g
$375 CASH
--have a cloth for wiping it down, it is going to get a lot of fingerprints
--have an effective way to show it is clear, zip-ties or chamber-flag
--if someone isn't interested in a trade, drop the subject