I have to say that I offer no financial incentives, I just stick to a well tried & tested formula..
I turn up on time, I do a job that I hope exceeds the customers expectations, I take time out to put the world to rights with them, maybe even have a laugh, charge a fair price, leave a couple of spare cards and ask them to mention me to their friends and family if they're happy with the results.
Probably brings me 80% of my work. I've always known 'word of mouth' to be the best form of advertising.
Les