I mean, when I'm going to buy pins from a stranger's house, I usually checkout the house/neighborhood on google maps. And almost every time the seller has a house much nicer/newer than mine, located in a good neighborhood. Seems like most pinball collectors are pretty well off. Plus, buying or selling I always try to talk to them on the phone before the meetup. You can get a real good sense of a person with just a simple chat.
Also, I mostly buy from Pinside or Facebook ads, and so you get a lot of extra information about the person you're dealing with. Feedback history on pinside, or PII (like their name, employer, ect.) on FB. And really, once you've done a few large-cash deals it becomes old hat, and just how pinball business is done.