You can generally figure out this kind of scammer straight off - as soon as the deal is agreed and items n money in place they will cancell and say - "wwops, trade lagg"; "Oh noez, sry mora maney!11"(ty tsu); "no.. 2kk and 1 met plx!" (this is what they tried with me).
After that you just play with them - i messed around with them for 15 min saying shit like "oh noez, i forget the met, lemme cancel", "put ring there first", "sorry trade lag", " 1 sec leeme ask my friend if im not getting ripped off.. 2kk seems expensive for an atck ring.. wait plxz", or just offer 2 silver whenever he pts the fake one down.