New Post: Identify link source

Some years ago while I was in a retail environment several of our vendors provided our store with code we could insert in links to their shopping cart that identified the referral as coming from our store. I wish I would have paid more attention. I now have a need to do the same thing on a website. The vendor needs to know which of its retailers provided the link to their shopping cart so a commission can be paid to that vendor. How do I do that?

Steve