What do you look for in the corals you are thinking about purchasing?
If they have palytoxin or not. Just health of the corals. Honestly, for SPS, fresh cut is fine with me as long as the specimen itself looks healthy. I immediately break them off their plugs anyways and remount them on fresh ones when I get home. For zoas/LPS, I would look for healed frags.
What do you bring to carry them?
Small bag cooler
What questions do you ask the seller?
Lighting, flow, water parameters, etc.
What do you do when you get home?
Bomb those frags until they are radioactive! I dip the heck out of all the frags. Trust no one!
Like mentioned before, bring cash, ask for deals if buying multiple frags, bring a white LED flashlight if you don't run an overly blue tank as everyone's setup will be starkly actinic heavy... except for that one oddball that runs more white light.