Auntiedote; Although I generally disagree with you on several points, I'm not putting shit on you with the following comments. You do raise many valid arguments, although I feel on some issues you may not have the experience necessary to draw such generalisations. Sorry if that comes across as patronising, its not intended to be.
I am speaking from experience unless otherwise stated, and although I cannot speak for BT, I will say that I too have seen very few pills which give an
uncharacteristic MDXX reaction with either fresh Marquis or Mandelin reagents. Over the past year I've found less than 5% of pills/powder I've seen tested have indicated things other than MDXX. On two occasions I have seen what I have believed to be an unusual reaction and advised the owners not to take the tablets. On one occasion this advice was heeded, on the other not so. User reported the pill to be a very weak dose of an MDMA like substance.
First of all, many things can fool the testers, but experience with the testers often reveals such a reaction to be "out of the ordinary".
As to whether there are things substituted/added, IMHO of course there are. As too how often, on what scale etc., depends on many variables, not least product availability at that time. Safrole is definitely a product that
can fool the test (see
this post for pictures) but the
permanganate test (still in development) should detect safrole. Any pills which smell have safrole/isosafrole in them - intentional or not - as pure MDMA has next to no smell.
As for the effectiveness of testing reagents; no one is saying there are not serious limitations with the kits. But I believe that in a typical test if Simons is used with Marquis and Mandelin, and additives like safrole can be checked for, the procedure can be a good indication of what combination is likely to be there. It says nothing about small quantities of unusual additives or impurities, but in the hands of someone experienced, it is generally a good
indication of
likely compounds present.
Of course there's nothing to stop people adding poison to a pill, although any such move would not go unnoticed for very long IMO. In reality, even owning a GC/MS wouldn't guarantee someone would know every compound in a sample. If you don't have the appropriate "signature" the result is meaningless, as would be any result in the hands of someone who didn't know the art and workings of the technique. Of course we can turn to techniques such as 3DNMR, IR spec and x-ray crystallography to determine such things, but if you didn't understand the principles of operation...
What I'm saying is that while pill testers are limited in both their selectivity and limits of detection, in the hands of someone experienced, anomalies are noticed. One thing pill testers should be - up there with GC in a way- is that results
should be repeatable between bottles of the same reagent. Many techniques such as HPLC can tend to produce variations between machines, requiring the need for standards calibration. When all this is considered, in the hands of the average informed user, simplicity and ease use makes the kits quite an advantage over the nearest alternative, at this stage anyway.
To paraphrase what Johnboy has said many times; sure kits have limitations, but at present they're all we have.