That's why education is so important when you're paying the amount we do, especially for coke. I'm off the beans now, but it's just obscene what rack passes for it these days.
Put the word out that you're informed. Let the sources know that you know the basics of testing cocaine - the acetone wash, the bleach test. Costs you nothing and you can see within a matter of minutes the kind of rubbish you have in your little baggie.
I picked up the Cocaine Users Handbook on Le Junk's recommendation, cost me a pretty penny to get it shipped across from the US but got it before the dollar REALLY tanked. It's an absolute revelation as to what goes around these days - coke is the real flavour of the summer and it'll probably stay like this for a while.. everyone's trying to catch the wave and make a buck, all at the detriment of the end user.
Stay safe out there guys, it's not going to get any better. Reward those who look after you and punish the bastards who fuck you around. Leverage your buying power. Sure, they won't miss one guy, but if you, your other mates who use and their mates start looking around elsewhere, it's a sizeable income stream that's walking away. The sooner everyone knows the basics of testing what's going up their nose, the better it'll be for everyone.