Good-Person
Captain Junkie
If your business renders a high quality products and services to your customers, they will be satisfied. The chances they are going to refer your business to their friends is very high. They don't need an incentive to refer anyone to your business.
This is also one of the marketing strategies many businesses use. They also offer gifts to customers and rewards when they refer customers. In many cases, many companies also start a kind of offline referral program as well. In such cases, anyone (including the customers of the company) could potentially become partners with the company and earn by referring other customers.