Hey Noob.. I've tried this a few times.. Sorry not your Script but it pertains to a script such as yours so i thought id respond here..

is it possible using LUa to make the NPC do a check for a certain item in persons inventory and remove it upon completing the function.. Ie you need a Runed copper rod to be buffed with Str.. After buffing str it removes 1 runed copper rod from players inventory?.. I know thats a stupid example but its just off the top of my head.. or perhaps maybe even simply gold?....