From the promo code page in the panel:
"The only downside is whatever discount (new! and/or feature bonus!) you give them comes out of your $97 one-time rewards payment (anybody who uses a promo code will be set as a one-time rewards, not recurring). But hey, that's only fair! It's basically a way for you to share some of your rewards with the people you're referring."
So you will be set to a one time instead of 10%, and you reward will be minus whatever you give away. Hope this clears things up for you.
art.googlies.net - personal website