Copied straight from the marketplace rules:

Disclaimer:
KWWHunction is not liable or responsible for any transaction made. We are only providing means to enable webmasters and users to trade amongst themselves. If any problem occurs, please report them and we will do the best we can to rectify it, although we're limited with what we can do.

However, as you all know, we're bound to face a few scammers here and there. So use your web smart to figure out if this is a good trade or not.
EDIT: This basically means if the sale/trade/whatever has been done on KWWH and you got scammed, just send a PM to a staff member with enough proof so we can ban the scammer, no need to make a topic about it or w/e.