I think someone hit it on the head... request a FaceTime live (or some other live venue)for the machine. The seller would need to show the machine... and their face.
They could do a live zoom, YouTube or other way to do a live feed to verify. Another idea is to have them show a piece of mail for the pick up location. Like an electric bill. I think by combining those two things it would make it tougher to get scammed.
FWIW.... before this thread it would have never crossed my mind to do these things. So thank you for posting!