If you are doing your job and always providing excellent service for the client, then you will get referrals. People will always remember someone who went the extra mile for them.  So do I give my clients a incentive? Yes. I provide service over and beyond their expectations. I have customer service call them after the work is done a couple of weeks just to say thank you and a quick check up. 

Personally I would ever recommend someone if I have never had dealings with them first. No matter how much they were offering.