I get scam crap in the mail all the time at work. Some company or individual from another country trying to get a "U.S. Connection" for his scam, bla bla bla. Anyway, these are totally unsolicited mail scams that I get so here's an idea. Why doesnt the Source include a letter in all of his packages similar to this.
"We have noticed your interest in health and fitness supplements and have sent you the following package to try or sell at your own risk. We will be contacting you soon to see if you want to continue moving our product in return for payment or supplements."
Or something similar that could cover the buyer's ass. This would give the buyer a window to say "Hell i dont even know who this is, I didn't order anything like this."