There are tons of bogus supplements out there.
Just listen the typical AM radio infomercial on a Saturday morning:
The script:
-they "discover" a dietary need that you're not getting from food
-if you take their stuff, you'll benefit from a list of "feel good" responses
-they will replay "testimonials" from previous customers or actors
-they never present an objective, double blind scientific study to prove their claims
-that stuff you buy at Wal-Mart is NOT equivalent; only their "potent, pure" version works
-they will offer a "free" sample if you just give them your credit card information to pay a small fee for shipping
-then they will start shipping you a supply that will cost about $30-$60 per month each month without your permission
-when you call their customer service to complain that you never agreed to order the stuff, they will not answer the phone
-you will go through hell with your credit card company to stop those recurrent charges
rinse, repeat