Someone else came on the forum a while back asking about this very same thing. I tried searching for the post, and couldn't find it. At the time, I remember thinking that getting paid that much for a drug screen seemed ridiculously inflated. With your question, I Googled it in various ways, and the results were less than positive, no pun intended. There are definitely some problems....and you will see that if you Google also. Basically, if I am understanding what I am reading correctly on various websites, the whole thing is considered a kick-back scheme between the facilities and the labs involved, and insurances are on to it, as well as fraud investigators. Drug screening in general is on the radar, it would seem.
EDITED TO ADD: I found the previous post, because you replied to it, below this post you started, lol!