Fjones-- Good point. I'd suppose it depends on the party. When I was still doing work for the local branch of RaveSafe, the larger promoters were always very happy to let us do our thing. Which included testing pills for people. For legal reasons we weren't permitted to handle the pills that we were testing, but rather we would go into a bathroom stall with the person, set things up, and walk them through the process with our kits. Luckily we never had any harmful pills (this was still during the time of DXM pills), but more than a few bunk ones.
My advice-- never never buy pills at a rave. Buy them at your leisure, and if possible test them in front of your dealer before paying. A decent dealer either will have already done this, will want to know the results anyway, or has enough confidence that it will pass. If they won't let you do it, then don't buy.
Know your sources. Cultivate good sources. Exercise your free-market right to refuse to buy.
Dtergent-- Ugh, I know the feeling. Still, I've yet to see a picture where you looked less than stunning.