This is one area that is often overlooked as an “out of my hands” part of the affiliate marketing funnel. Once you’ve sent a visitor to the merchant site, all you can do is cross your fingers and hope they ultimately complete whatever action is necessary for you to get your commission. That’s partially true I suppose. But you have more input here than you may realize.
For example if a user follows your link and looks through an online software store they are tracked as "your referral" by the browser cookie. If the person makes the purchase before the cookie expires, you get the referral commission. So even if a user sits with items in their shopping cart but doesn't go back and make the purchase for two weeks, you can still get the commission, provided the cookie is still active.