Based on the secondary research redlaser provided quoted below the lack of standardization in the THC testing industry is a major problem. There is a complete lack of consistency in testing among growers, dispensaries, labs, breeders, etc. etc. which makes testing nothing more than a joke. But, on the other hand I want the bomb shit. If your puffing it and its not getting you ripped, well, thats a problem!
I see what your getting at. I have also noticed a discrepancy among tested marijuana. The high numbers could potentially be creating a placebo effect.
Gas and liquid chromatography tests are the most common, as long as instruments are calibrated and operated correctly the results should be the same.