Who was Brett Anyway?

About the only thing that sticks with me as terribly incongruous about Pulp Fiction is wondering what exactly were Brett and his buddies doing with the apparently very valuable property of Marsellus Wallace. They come across like a bunch of not terribly competent college kids, way out of MW's league.
So what was he doing having Brett and his buddies even working for him in the first place not to mention holding that briefcase?
-Tom Toren