I don't have any sources to cite, but with my graphic design business I give discounts or cash for referrals. Although just telling people doesn't really seem t

I don't have any sources to cite, but with my graphic design business I give discounts or cash for referrals. Although just telling people doesn't really seem to do the trick. Instead, get them something in their hand that reminds them about it. I like to use something that is akin to a coupon, but really well designed and on heavy card stock. Perhaps even embossed or foil stamped... all depends on what your marketing dollar looks like. Probably not the end-all solution you're looking for, but a small hint from my experience. Goodluck!