RJW gave the best description overall.. I can throw in some of my advice..
1) If it's ROCK SOLID and NOT SOFT AT ALL thats good.. re-rock may be in a rock form, but it will usually crumble fairly easy - ie you can crush it with your drivers licence .. pressed coke from the source is solid, you could throw a rock at the wall and it wouldn't break ..
2) Color doesn't mean shit - so just forget all you have heard about "beige is oil based and it's not as good as the ether based which is white because it's all made in areas where the moons gravitational pull is stonrger in turn drawing all the impurities out of the coke leaving it white" (or whatever the local CaNdY RaVeRs are telling you about buying coke)
3) Nubness doesn't mean shit - you can buy an ounce of a cut for about $20 that will numb you FAR MORE then totally pure coke - my roomate picked up an ounce of this to cut his coke with and just for fun we went to a strip club, he wanted to give the girls lines for free just to see if they noticed it was 100% cut or if they were slightly thrown off because it numbed them - he started out GIVING AWAY free lines but several of the girls said it was the best coke they ever had "because it like, totally numbs my whole face" .. he sold the entire ounce to the girls at $50 a gram, all in under an hour - thats right, because it NUMBS YOU BETTER THEN COKE these girls didn't seem to notice it was totally devoid of any "high" - it just numbed you! And PhreeX will NOT give out the online source for this, because he knows you guys would just be dishonest with it and take your $20 investment and use it to rake in $1400 in money.. DIRTY MONEY - how could you fall asleep infront of your new digital TV knowing it was bought with DIRTY MONEY? Sorry, I won't post it! (though if someone else does, I can't delete it as you're not breaking any rules! It's only "inscense")
4) In all honesty, what you get will most likely be cut - at that level thats how the game is played.. if you're only buying an eigth of an ounce, yeah, it will be cut or re-rocked .. so the best thing you can do is hunt for he who cuts his shit the least, then give him your repeat business letting him know its because of his QUALITY - even if you have to pay more (and you most likely WILL) ..
Sorry I gave so many "don'ts" when you wanted to know HOW to find good coke.. I guess the answer is you just sample - do a bump or small line and see how it effects you.. ignore the numbness factor and focus on the energy it gives you - if you have done coke then you know what makes good coke good - look for that!
Also, the TASTE of coke is kinda a hard thing to fake, though even when cut, enough of the taste will remain - so something to consider is that the stronger it tastes, more then likely the stronger it is... still, it's that sample you do that lets you know ..
Oh yeah, the myth about using Clorox Bleach to test for purity is just that - a MYTH! no truth to it, it's bullshit!
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"I am not one of those weak-spirited, sappy Americans who want to be liked by all the people around them. I don't care if people hate my guts; I assume most of them do. The important question is: 'What are they in a position to do about it?'" (William S. Burroughs)