All but two of my bows were bought on classifieds (AT). Like anything, do your research (feedback system is in place over on AT, so that's a plus), and be smart about it. All of my experiences have been great.
Try that on a U.S postal money order from the post office. watermarks and scan bars not so easy to reproduce. it's not like a cashiers check or the money order from the local 7 eleven. Ten years and i never been burned..
I've bought and sold probably close to 300 bows on the internet (literally). Mostly selling, but I've bought probably a couple dozen too. I use to help a local shop by buying all of their used and dead inventory, and then I'd resell it all on the web to make a few bucks. I think I've actually sold several bows to members here years ago when I was doing this. By far, the best way to protect yourself is to use Paypal, and UPS. I've processed a handful of disputes on paypal as both a buyer and seller, and they always have resolved the situation for me. It may take a little while, but they have always made things right for me. UPS has screwed me a couple of times, but it was a lesser amount of times than USPS, and their tracking process is much more detail oriented, plus I always found their service to be much better. Just my thoughts, but it's coming from someone that has moved a LOT of gear to people on the web. The only deals that I've been really left out to dry on were check or money order deals. Only paypal and insured UPS for me.