LC has really summed it up for you very well - treat folks as though you'd treat them in real life versus as a couple characters on the monitor and you'll be fine.
Assume the best, plan/ prepare for the worst. If it feels funny, don't.
I like paypal, it's easy and really, the bitch about the fees is ludicrous. 3% is what you will pay to accept credit cards and so be it. I have to ask you to send your knife first, I have no business trading with you - see the last bit about if it feels funny.
I'll add one more that I ALWAYS live by. If you cannot afford to take the money you are about the spend out on the sidewalk, pour kerosene on it and set it afire, you have no business doing this transaction. What if it goes bad and that is some sort of weird fubar'd deal you are working for the mortgage or the car note money you are short?
We expect it will go well and I'm trying to recall if I've ever had a bad deal at BFC - I do not think so. Keep in mind your idea of New may be different than someone else's, and so forth, so always be as honest and up front as you are capable of being, and always be prepared to undo the deal.
I did have one trade a while back, back in 1999 or so, which I made a mistake on. I was called on it, and it was simply a lack of understanding on my part - as a result, I'm very careful to make sure to be as up-front as possible when I put a knife up for sale.
One other thing - IT'S JUST KNIVES! Nothing here is worth a heart condition. Or a bad rap. No piece of steel is so important it's worth screwing yourself to the floor over.
And have fun - we've all become better for the experience, and I have a really cool knife collection as a result.
Welcome to the "real forums"

and I look forward to swapping steel if we can find something we simply cannot live without in the other guy's sock drawer.