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).
Once you've protected your prospecting pool, maximize your affiliate program by working with the best and leaving the rest. As the old 80/20 adage implies, most of your revenue will come from a very small percentage of your affiliates. Because it can be time-consuming to manage a larger affiliate network, consider selecting only a few companies initially, and interview them before signing them on. Affiliates are an extension of your sales force and represent your online brand, so choose partners carefully.