Couldn't you have not gone through with the deal?
One time I was trying to cop on the street and I gave the guy money for 4 bags and he handed me 4 crack rocks. I then was like, "No! Heroin! Not this!". He wouldn't give me the money back, but the price for 4 bags of heroin was more than the 4 crack rocks, so he did give me the extra money I had given him back, which was kind of cool because he could have easily just taken it. Was still annoying to have crack instead of dope. Plus, I was like, "Now I have to smoke crack." I don't not use drugs.