I won't say that it can't happen, but I will say I bought a lot of G1 Transformers stuff last year on the Sunday afternoon after a ton of people already had a shot at all of it.
Nevermind the vintage complete Mork for Ork with his Eggship I scored on the Sunday at closing time as well.
I find that a lot of people don't dig around at the dealer tables that belong to collectors and that there is often something cool to find in the bottom of a box.
Also Raven Collectibles tells me they are bringing a huge assortment of in box G1 stuff they aquired recently.
Anything your looking for specifically?