well, if your herb doesn't smell like herb right away, i would stray from it... and if it smells like there is a foriegn substance in it, don't smoke it... if you buy a bag of shake or loose herb take a pinch... most of the time herb has moisture in it... and culinary herbs are almost always drier than hell (i cook alot)

keep smokin and tokin man, and you will just know... also don't forget anyone that sells oregano... is a straight up punk... it is complete disrespect... find yourself good, reliable, laid back smokers, and you will find your weedwiseness will grow

PS:no matter if you got sold real marijuana... if you aren't high, and you know you have taken, and held in some REAL hits... complain, get your money back, or warn other mother fuckers...