Yeah and I perfected this exploit so you don't have to do the damn switcheroo with the gems.
1.) Open the trade
2.) Insert the Gem into the weapon/armor
3.) While in the "Cast", get the used gem into the trade window
4.) Wait for the "Castbar" to finish
5.) Now the easier part...just cancel the trade and bam
6.) You got the Gem AND the Gemmed Weapon/Armor at once
+REP ?