You would be wary with only one feedback? You know what? Take it from somebody who has sold a LOT more stuff on the internet than you have...if you are out there, on ebay or whatever, and you do any amount of volume at all, you are going to run into that one in every five hundred people or so who is just downright NUTS. Sorry, but that's the way it is. And you can bend over backwards, give them two for one, double their money back, and a backrub, but they will STILL give you a negative feedback. Just how it is. Thankfully, they are only a small percentage of the world, but they ARE out there, and as soon as you run into one, it will burst your incredible bubble of ARROGANCE that would make you make a statement like the one above.
Sorry, but your statement disturbs me. Guess what: You can do everything RIGHT and STILL get negged. That's how it is. In the old days, people would walk into your store, and you could get a face-to-face assessment of who the customer was, but nowadays, you just don't know. There are some real NUTJOBS out there. So don't say "I am perfectly honest, so I will never get negged" and "I would never buy from somebody who has a neg", because you come off sounding facile, naieve, and inexperienced.
And your advice about Paypal shows that, too. It's dead wrong, and it could cost this guy this jet.