Idunno about meth specifically, but I do know that smoking weed thats got x, dxm powder or coke in it gives it a really rubbery taste that you notice right away and after a few hits your mouth goes a bit numb, it's unmistakable.
And I really must advise against buying from people if yer worried about them drugging you, though, I mean I know we've all done it but still...