Since this is a business rather than a job, it’s difficult to quantify how much you could make.
Typically though, referral businesses work in one of three ways: they charge a fee from the business that wants to be a member (typically around $200-$500).
Or, they charge a fee from the consumer for getting their list of recommended businesses (typically anywhere from $10-$50, though presumably, if the information is valuable, you can sell many more of these than of the former).
Or, they provide both services for free and rely on advertising to pay the bills (especially if they are on the Internet).
Some people who run a referral business try to combine all three.
Therefore, how much you can make depends on your niche, how valuable your information and your referral is and how many people will care what you recommend.