It probably is, but that does not stop people from effectively doing it. There are a number of groups that specialize in conducting group buys, doing a bunch of testing on randomized samples, and then shipping out the product to individuals.

Also, if you plan to be on it a good long time, you can buy a bunch of kits yourself (a kit is 10 vials), run a bunch of tests, and then just have a nice stockpile that will last you years. The testing will likely cost as much or more than the product itself, but given how inexpensive the product is, you still come out way ahead financially.