If you refer someone and they end up commissioning a piece, I'll give you 20% of the selling price.
Refer three or more people to me, and I'll gift you a small (24" wide-ish) painting based on your input.
Enter in your email and mailing address and I'll send you some business cards and a bit about how you can make your friend's walls much less empty.
Art is better when more people actually know about it. A referral program helps spread the word while making sure that my friends get a little love back.