first you need any get either super or refined and then say selling bla bla bla gem
when some one asks to trade put up the gem and then cancel
trade again but this time put up the same type get but lower lvl
example if you put up a super dragon gem put up a refined one the price difference is alot and if the buyer doesnt notice the change they will be buying a refined gem for the price of a super one
hope it works






