How to avoid a scam - don't buy anything lol. Basically don't buy anything you can't physically look at first but if you choose to ignore that advice then BY GOD use a CREDIT CARD. One phone call and they will get your money back.
ALWAYS expect the worst and you'll never be disappointed is what I've found. Some people just don't know their asses from a hole in the ground. They aren't lying - they just don't know any better which is frustrating as hell. "Yep, everything works". When you finally get it you find out everything is just worn out, missing parts - hell I had a pin show up with a missing board - but was told it was all in working order. That was pretty shocking to say the least. lol