Software

My idea is create a web site like ebates. I can do the design and insert the affiliates links (short codes) but i don't know how I can track who purchase anything trough my site so i can reimburse them. Example: I have a site with lots of banners: Walmart Amazon Best Buy Etc. To access the banners people have to register in the site (like ebates) I will receive commission from the affiliates for people who buy their products using my site. And I want stimulate people to buy giving them cash back after a minimum purchase amount be reached. (Part of my commission). My problem is: When people click on a link on my site they will be redirected to the merchant site and do the purchase directly with them. As far as i understand, each affiliate program give different feedback for paying my commission. How can i know who bought what and where using my website? I hope you can help me with a solution for this. Please let me know if you need more information.