It depends on how much time you want to put in. For a longer term strategy, segment your list and promote relevant products to them via emails - Also, when applicable, generate leads for the businesses being listed. You just put your affiliate ranking higher than all other competition, and put emphasis on his listing.
For example, lawyers. When a user comes to your site looking for a lawyer, you have the power to decide who they should see first. Lawyers are happy to pay good money for your leads, if they are authentic.
So in addition to selling them leads, you can also sell relevant products to them. Email marketing services, testimonial services, logo-redesign, ect.
Be creative. Business owners have money and can often be convinced to give you that money - just be sure to focus on providing REAL value and not just making a quick buck. If you can keep providing that value, you will be able to make money from them over and over again because they will trust you.