A dump store is exactly that, LilPaintballer, it's a store that GS just sends all the older games into when they don't want to deal with them or don't feel they're selling in a particular area anymore.
For example, I know there's THREE of them around my area, with one being 20 miles away, the second being 30ish and the last one being over 40-50 miles from my house. I've only hit the second and third ones when I'm down that way for work or when my one friend wants to take a road trip.
Either way, I've found some good stuff in some of the stores, stuff like:
Saga Frontier II
Devil Dice
Wing Commander IV(discs 1,2 and 4 only dammit)
And just tons of other games that I either had once or wanted to try and hell, at the prices they're only going for now, how can you say NO? Of course, you still have to check condition, since many times the discs are seriously

ed up looking. I turned down a Tobal No. 1 last week alone for the fact that it was ALL scratched to shit.
You just have to hope that your local GS managers don't pull a bs like the one closest to me did and say they dumped the dumped PS1 games off on another store but cherry picked those things first, finding stuff like Persona and other good games prior to sending them out.