I know of this, but prefer to trade here.
otc means over the counter. a trade here through the forum is over the counter. you can trade anywhere. but when you use the web of trust, you can see the person's trading history, and after the trade they can rate you so that you have a documented strong rep and trade history. it is optional for any trade and costs nothing other than a little time spent authenticating before you trade.
well, looks like you got your trade, but keep it in mind for the net time maybe?