Affiliate commissions are tracked using cookies.
The first time someone comes to the AWeber site, a cookie is set that denotes which affiliate referred that person to us.
When that person orders an account, we check the cookie and assign the commission to that affiliate.
What If 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.