Of course, cash is person is best in an ideal world. However, for us folks in small markets, buying machines through PayPal and shipping is often the realty. I typically only look on Pinside, will only contact people that have had accounts for over a year (and check their posting history). Once a potential deal is lined up, usually through PMs or text, I like to Facetime (or atleast call) the person to see their game live. I always use my Amex through PayPal, and don't use the friends/family option (I pay the fee for the seller). I also notate in PayPal exactly what I am purchasing, and that once the machine is picked up for shipping (which I arrange) the seller is no longer responsible and the machine is sold as-is.
It's probably not a perfect system, but it's the best I can usually do without driving 5-10 hours one way. The games I have bought from Pinside typically end up in better condition than even described.