The phrase, "Affiliates are an extended sales force for your business", which is often used to explain affiliate marketing, is not completely accurate. The primary difference between the two is that affiliate marketers provide little if any influence on a possible prospect in the conversion process once that prospect is directed to the advertiser's website. The sales team of the advertiser, however, does have the control and influence up to the point where the prospect either a) signs the contract, or b) completes the purchase.
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.