In affiliate marketing, first click is often used to describe an affiliate program where the first affiliate to get a user to click a link and make a purchase within the limits of the cookie expiration is the one to be credited with the sale, even if the user landed on another affiliate's website and actually converted after clicking on a link from the second site. There has long been a debate between whether first click or last click is most beneficial to both the affiliate and the merchant.
You should also make sure you aren't competing with your own affiliates for eyeballs. Any marketing channels you're using, such as search engines, content sites or e-mail lists, should be off limits to your affiliates. Put marketing restrictions into your affiliate agreement and notify partners immediately. It's your program--you set the rules. Or, if you prefer, you can let your affiliates run the majority of your internet marketing.