I think he means if he sells the weed for him and gets the guy at least 80$, then the guy will give him 100$ worth of weed. If that's it, then the guy is ripping himself off, but I can see why, if he doesn't want to get caught.
Oh... Well I suggest splitting it up into 1/4 oz, depending on how much the guy actually gives you. If he's true to his word and is giving you 100$ worth of weed, make two 1/4 oz worth 40$ each, or make four 1/8 oz worth 20$ each, and then you can save 1/8 oz for yourself. I think 1/8 oz for free is pretty good.
Hopefully you listen to me, I know a lot about my shit.