Yea, I don't know about #4. Personally, I wouldn't let a prospective buyer load a pistol (ever see Terminator?).
I dry fire the pistol, and with the trigger held back, push on the top of the chamber. If there is a lot of movement, it's pretty worn. If there is just a little, less so, but keep in mind, even the new guns will have a little play when you do this.
It's usually not hard to see if a pistol has been taken car of or not.