Yep, things happen once in a while.I have sold thousands of items and had very few problems. Paypal is the way to go with the payments, they will even back you if someone rips you off. Before Paypal I sold hundreds upon hundreds of items and they simply sent a check and then I cashed it and when it cashed I mailed the part. One day I joked to my wife how I had found a way to distribute our address so people could send me money.
No kidding, that is what it felt like, it was soooo easy.
Well, now Ebay gets a little bigger slice, and with all the "stores" and retailers and crap it is a cluttered up mess compared to the simple amateur auction site it was when I started in 99. But it still works pretty good. I bought a bunch of stuff for the Rambler when I was doing it, NOS brake shoes wheel cylinders, shocks, An NOS horn button, I bought all kinds of stuff for it. A crap load of stuff I have for my Gran Sport and all the 53 Corvette motor stuff I am collecting for my truck, all on ebay.
One of the best things you can do is to set your expectations a little low. Say you buy a blower manifold, no matter what the guy says expect it to be just a little shy of how good he tells you. He says there are no stripped holes, expect there to be at least one, you know what I mean? That way when it comes and there IS one, it isn't a big deal you have already accepted that. If it comes and there are no stripped holes you are THRILLED. That is how I look at anything sight un-scene. My brother will have super high expectations and no kidding, over all these years he still does it and often gets disappointed, you have to set your expectations lower. If you are ok with that manifold with one stripped hole you need to fix, they be ok with it and buy it, if it has one you fix it if not you hit the jackpot.