Hmmm, he "graciously" pre-busts the weed up for you? Awww, how nice. It was porobably a little bit of weed mixed with some random green, cooking herbs. Never, EVER buy grounded up cannabis, for that exact reason.

Always buy nugs and always look at it before you buy it. Don't be surprised if he gives you nothing at all. Learn from this mistake and move on.