Be very careful. Scammers now have new methods.
A few days ago a guy on the BMX museum posted to say that some guy had shown interest in a Mongoose frame he had for sale. However, it was for his son and he asked to put his son's name in the proof pics. Like so.
He then vanished. I would imagine he was using a fake account on FB, as someone with that name who then went on to send his buyer those pics in order to get the money out of him. And I bet he succeeded too, sadly.
Thankfully for me all of my stuff comes from knowns. Either Ebay, or through groups where I personally know and have met these people (and most importantly know where to find them if I ever had to).
But do be aware that any ideas people get for proving people have stuff for sale can also be manipulated and turned around by the scammer. Who will outthink you, and try to outsmart you. And that evolves, as scamming does.