Karin,
The thing about live sand coming out of a mature tank like yours is that you mix the different layers of the sand, which kills the sand. In actuality this makes the sand toxic if you were to put in someone elses tank without washing it thoroughly. You might have a hard time giving this away, much less getting someone to trade for it. Best of luck though.
-Kris
hmm, i actually only used to the top levels (looked very clean to me)
...actually tradet already half of it to some experienced guy
so you are saying that this was a mistake and he shouldn't put it into his tank??