Well it's definitely not sure fire, but there are ways to tell you didn't get completely ripped off. Where are you trying to score?
SMELL - I don't know to what extent smell plays a part in East Coast dope, but here in the West the shit usually smells STRONGLY of vinegar (not really vinegar but the closest describable thing I can think of). Once you smell it for the first time, you'll always know what to smell for.
TASTE - Couldn't really tell you since I don't know shit about the taste of East Coast shit, but my guess would be it doesn't taste good. Probably make your face pucker up. Black tar heroin tastes like asshole. If you're smoking it, it's really hard not to gag and I always need something to chase it with like soda or something.
SIGHT - Now this can get tricky, because when dealing with brown/yellow/white/off-white powdery substances the eye isn't a very useful asset. The general rule of thumb is the brown clumpy shit is the most pure. Everything else, depending on color is more heavily cut. This isn't to say that there isn't really amazing white/off-white heroin out there, but typically this is how it works.
For a good idea of what to look for, check out this link:
http://www.erowid.org/chemicals/show_image.php3?image=heroin/heroin5.jpg
It progresses in purity and cut from TOP to BOTTOM. That's to say the Brown clump shit on top is the best and everything else is more heavily cut going down.
As far as
black tar, shit it looks like funky shit. Sometimes it's a nice pliable gooey tar kind of like opiun and sometimes its more of a rock that needs to be cut into pieces as opposed to being gooey enough to be pulled apart.
Hope that helps...
Lemme know how your quest goes, if you're on one...
[ 20 February 2002: Message edited by: EvilSpaceMonk ]