Let me confirm something you already know on a gut level; the supplement industry is a capitalist's wild wild west, a profiteers paradise, an unregulated free market, and consumers should beware.
While the ubiquitous white Nutrition Facts box you see on the labeling of packaging looks official, anyone with basic word processing software can create such a representation of the ingredients ostensibly in a product.
When you realize that no one verifies that the actual individual ingredients are in a given product, you realize how much of a decision to buy and take an supplement is based upon trust.
The Nutrition 'Facts'
When supplement companies sell products to consumers they can almost count on the consumers not verifying what they are consuming. Sure the consumers could send products off for testing at 3rd party laboratory but that costs between hundreds and thousands of dollars. While there are some consumer spectroscopy devices coming to market that promise to disrupt multiple industries that prey on the voracious consumer, at the current time consumers have virtually no way of personally determining what they are actually putting in their bodies.
The good news is that one of the really easy ways to make almost certain that you are getting the real stuff is to insist on always buying Pharmaceutical Grade supplements. Why trust Pharmaceutical Grade?