I don't receive such things in my mail.
I also have a sign on my box that asks for "no junk" - to me that means any vendor ("charity" or not) - that is seeking $$ from me.
But if I did, I wouldn't have a problem using them. If someone sends me some product that I have not ordered in the hopes of getting my business or seeking payment for such product they can get stuffed if they think I should compensate them for their efforts. I didn't order your service, and maybe if it's a charity I don't wish to donate. Those are my prerogatives, and I don't feel any obligation because I didn't initiate anything. Nice try, you failed. Thanks for the free stuff.