How to ensure commission payment

I’m creating a business plan for a product that basically assists customers in early stage planning for new residential construction projects. When they get to needing a general contractor, I’ll recommend a few options and get a commission if they work together.

My question is how can I ensure that I get paid these commissions? I’m not really going to know if they end up working with the contractor unless the contractor is honest and tells me or I follow up and ask them.

Any ideas?
@dbreaker I saw that you had a similar setup with real estate agents for awhile?