I've never been sold bunk shit at parties.
I have been sold bunk pills and bunk meth by friends before. I didn't really screw over the guy who sold me the pills, because he got it from a "friend," whom I later found out didn't really know the guy. The guy who sold me bunk meth--a really lame individual who liked to talk shit about drugs--did it on purpose. After that, he asked me if I knew where he could get some coke, so I just put a mixture of baking soda and baby powder in a baggie and sold it to him. I've not heard from him since.
I don't believe dealers should sell people bunk shit. I mean, they're in it to make money. Why would they want to ruin their repuatation for a quick bunk?
Personally, I've never sold drugs (minus that one fake-coke incident). But even if I did, I don't think I'd sell bunk shit. In reference to the fake-coke thing: if someone's going to sell me fake drugs, then have the audacity to ask me to get them something, I'm going to screw them over. I mean, it's only happened once, and I don't really care about it, as I was going to end the friendship anyway. He totally deserved it.
As for the friend who sold me fake pills, I couldn't really blame him. It was more my fault for buying it, even though at the time I had thought they were pretty good friends. I mean, it was supposed to be MDMA in a gel-cap. For that reason, I will NEVER buy gel-caps again. It's just too risky.
I do blame myself for the fake meth; I should have asked to test it first. But, I got revenge...so it's no big deal.
Buying drugs is risky. You never can be sure about what you're getting. When I buy stuff now, I ALWAYS ask about it: quality, what it's cut with, etc. If I'm buying from a friend, I generally ask to do a bump to test it. If they don't let me, I don't buy.