After quizzing them on the phone, it would seem this organization are calling regarding a "get rich quick" type of scam. They try and get you to accept their "free" product and you only pay for the shipping (cost of something like $2.95), then if you decide you don't want their product, you send it back. It is very reminiscent of the old Columbia House scheme where by if you didn't remember to send back the product or cancel your "membership" you were then automatically charged at whatever inflated price they decided to charge for their goods.
VERY, VERY aggressive, won't take no for an answer sales approach. I'm sure some people are bowled over by this and give in, falsely believely that they actually agreed to buy something when no such committment was ever made. The origin of these persistent, annoying calls *MAY* stem from an online form for information being filled out or alternatively from a farmed list.