This herb is supposed to improve memory, among other things. Of 27 brands of saw palmetto, which is sold for treating symptoms of prostate enlargement, only 17 contained saw palmetto in the amounts claimed. Of 26 vitamin C pills, four didn't pass. Of these four, one wouldn't dissolve, and the others had less C than claimed. This, alas, is meaningless.
Herbal products vary widely, simply because of the nature of the plants and the processing.
One batch of saw palmetto capsules, for instance, may differ greatly from another, even though they both come from the same processor. Tests for vitamins and minerals are more meaningful, since only one substance is involved. Even there, one sample doesn't prove much. The next batch might contain less or more. And it's important.