Done In The Rear

So I didn't have a chance to pick up smokes today and knew of a person going that way and thought I'd just have him and his girl pick up my smokes. This is how it's done when no one is looking. I gave the guy $15.00 and told him to buy as many packs of berry flavored cigarette cigars as he could and buy himself a pack for his troubles. They cost $1.50 per pack. He brings me four packs and tells me he spent $6 of my money on himself. This is a good example of contract law gone bad. We had a deal and he renegged on it. This is being done in the rear majorly.