My rules are simple: Meet in a public place(prefer my place of business). See an ID(or better, a CCW) to verify residency if I don't know the person. Ask "Is there any reason under state or Federal law that you would not be able to purchase this firearm?", again if I don't know them. Gut check: if it doesn't feel right, it probably isn't. If all of those things pass, then conclude the transaction, shake hands, and carry on.