That's what feedback (positive, I hope) is all about. Ganagati is correct, but you can also use Standard PayPal and it can help. However, don't use the GIFT option, which will NOT seek to help you with a dispute. You can normally have the option of sending PayPal standard (+3%) or PayPal gift. Don't use gift unless you know the guy or he has a great 100% Positive Feedback of at least ten; the more positive feedback, the better. I haven't been zapped yet by a deal, but I came real close. You can always ask for a 2-day non-cut inspection, but sometimes the seller will say "All sales are final." In this case, be careful. Of course, you can check out a knife in about 10 seconds.
And, of course, if the Seller has been a contributing (posting) member on this forum for some decent period of time, that doesn't hurt either.
I had a fellow sell me a knife with a broken, but poorly repaired, tip of the knife, and it was finally shown that the guy who sold to him was the scalawag. But I sent it into Strider, and they repaired it free of charge. When you pay money for a good knife, you're also buying the Customer Service. Pay attention before you buy. Of course, if it's a cheap knife, you won't stand to lose very much, but lots of decent folders run from $200-$400 or so.
Sonnydaze