Affiliate commissions are tracked using cookies.
The first time a potential customer comes to the AWeber site through an affiliate link, a cookie is set in their browser which denotes which affiliate referred that person to us. That affiliate link might look something like this:
When that person orders an account, we check the cookie and assign commission to the affiliate that referred them to us. A cookie will remain attached to a potential customer's browser for 365 days unless they clear their cookies, or have software set to do so automatically.
You can see any current commissions under the Commissions section of your affiliate account:
What is someone leaves and returns through another affiliate's link?
We award the commission to the affiliate who originally referred the customer to us. Their cookie is not overwritten by the customer coming back to the site later through someone else's link.