Would have to unsocket it before trading, obv the jewel is useless, but if it has +defense on it to account for non perfect base defense, someone could easily be fooled.
That's why I said give them the hel+tp scroll.
The only jewels that should go in a griffons are a 15ias/15res, -5/5 facet (now, a -10/10/5xp lightning jewel).
I would immediately tell them to unsocket it.