It's a hard situation when all your expectations are dashed by a bad pill test.
Hopefully you've tested the pill at the time of purchase (not always practical or possible - but if a dd won't let you test the pill... find one who will) so if it tests clear or orange or green or... notpurple (provided you're after MDMA), then you can hand it back. Often the seller is just as interested in the EZ test result as they may not have heard of, or had access to an EZ test kit.
However, if you're testing after the purchase is completed, then you get a bad result you're kind of outta luck - not too many dds have a money-back policy (and the ones who do... you know who you are - we love you). It's tough because you've spent your dollars, but not got what you wanted, and you don't want to a. throw your hard earned bucks away, or b. knowingly sell a shit pill to someone else just because you don't want it (at least I hope that would be the case).
At the very least, I would personally chuck away anything that tested clear for sure - because it's just too much of a gamble. There may be nothing in the pill, or worse. If it tests orange, and you're willing to chance it, be really careful. Some pills going around lately (read: Yellow/Brown-spotted 69s) have been testing orange but giving strange user effects not similar to speed pills. Conjecture is going around as to their contents, PMA is a suspect.
As always - if you're not sure, either just don't take it, or take it by halves and be very patient - don't mix with other chemicals and don't hope for too much. And, to let a friend know what you've taken wouldn't hurt either.
Check out this thread "
Why do you test your pills?" for some further discussion on this topic. It includes information about where to buy EZ tests in Australia, and other assorted gems.
BigTrancer