Jerry et al,
I've bought and sold lots of things, maybe 30+ transactions, over several years. I deal mostly at A'gon and boards like this one, where you may 'know' the people involved, or perhaps there is feedback from someone you 'know'. I've never had a bad transaction, or even a shipping problem, ever, in either direction. Use common sense, and you'll probably be alright. I won't deal on eBay. I usually won't deal with zero feedback (definitely not with negative feedback). I'll drill thru the feedback, looking for 'regulars'. I'll often get on the phone and chat a bit, and trust my instincts. I won't low-ball, nor deal with same. I'll rarely bother with anything that looks too good to be true. I'll time shipping so the package does not sit in a warehouse over a weekend.
All that said, if you can cultivate a relationship with a good local dealer, you can get all the benefits of that (sevice, support, auditions, no shipping risk, etc), and get probably get reasonable pricing so that you won't get hammered at resale time.