Because I will give it to someone who hasn't heard about it before and encourage hir to do the same someday.
Don't do that pls, make them pay for it, no one appreciates the gesture and loses interest fast.
Explain what it is show them how it works and if you do it right they will ask you to sell them some, i do it all the time and it works. now whenever i meet those ppl they keep me up to date on the price