Tracking online sales

I wasn't sure what section this applied to - so I'm going to put it here.

I am searching out clients who want to use my website for advertising and have found some.

I want to track sales made via the traffic I provide them, so that I can take a proportion of the profit they make on a product.

How can I do this?

Thanks,

Jack.

 

I think you can just use a tracking link, unless I'm misunderstanding what you're saying.