Refers to a product being returned or a sale “falling through” that you were already paid for. Since the sale didn't actually finalize, the merchant will deduct the amount you were previously given in commission for that sale from your affiliate commissions. In lead generation, this can also occur if the merchant decides the leads sent were unqualified or fraudulent in nature.
Amazon has spent years perfecting the art of online selling and you’ll learn a lot about online marketing by observing how they do it. They constantly test different ways of promoting products and have evolved their site quite a lot over the years. See what widgets they use to promote related products, watch how they use reader reviews, and see the way that they describe products.
The dollar amount of commissions an affiliate has to accrue before being paid. Some merchants set a minimum payment threshold themselves (to lower accounting costs by paying less frequently to people sending very few sales) while others allow the affiliate to do so (usually to avoid receiving frequent smaller checks and instead receive one larger one).
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.