I offer that as an option as well, but cash usually gets people more motivated to help. Especially if they aren't interested in any products. Cash allows me to open the opportunity to everyone.
I'm running into the same issue now. I've learned over all the businesses I've owned in the past, that you need to spend money to make money. I'm offering all my past hosts and guests, if once of them refers someone (can even be themselves!) who has NOT HOSTED with me ever, once that person...