Basically, all websites insert cookies on your computer to indicate that you came around.
Visitors to your sites are uniquely identified whether they buy something or not. Cookies remind the website that a visit was made even up to 60days and more in some cases.
These cookies help products owners and affiliates determine who is selling and making profit from sales.
Recently, it has been discovered that many affiliates lose money to other affiliates because of
multiple recording of a particular visitor through several links to the same business.
For example John Smith is a buyer or a visitor who wants to purchase a product but he had actually clicked several sites belonging to different affiliates promoting the same product. If John visits the affiliate sites of Peter who happens to be the last person he visited his site and then buys, it is peter that gets the commission.
I personally think one can do something about that. Buyers should be educated to always delete cookies before clicking on the affiliate sites.