Welcome to RFUK!
I agree entirely with vgorst. Very poor advice from the shop I'm afraid. Leo eggs can sometimes look a bit manky, usually due to too high humidity, but still be viable. Best to let nature take it's course if there's a next time.
If you can see the "placenta like" thing (the yolk sac) then I'm guessing the little fella is out of the egg. Don't cut off the yolk sac - let it drop off naturally. If the little'un is still alive I would keep it in a RUB (poly box) with damp kitchen roll as a substrate until the yolk sac has dropped off.
Unfortunately there is a high chance that the gecko won't survive very long and if it does it may be slow to "get going". Good luck.
Eublepharis macularius 7.18
Timon lepidus 2.1
Lygodactylus williamsi 4.0
Teratoscincus roborowski 1.0
Phelsuma grandis 2.2
Bellatorias frerei 1.2
Pogona vitticeps 1.0
Last edited by jools; 23-01-2013 at 10:24 AM..