Many merchants and new affiliate networks ask me about how to screen for affiliate fraud or verify new affiliates. Here's a good general article I just found that can be used as a basic guide. This would be especially helpful as an overview for new affiliate managers.
Affiliate Fraud - Affiliate Marketing Scam - "Affiliate fraud is time consuming, expensive and can seriously jeopardize an entire affiliate program’s business model. Affiliate Marketing is a great way for companies to broaden their reach on the internet but you need to be careful. The only way to fight affiliate fraud successfully is to meet the problem head on, with a comprehensive approach. The range of tricks goes from the traditionally unmistakable monkey business such as forced clicks, bogus leads, fraudulent credit card usage to the more creative and well executed cons such as posing as webmasters of high-profile websites and changing their name and address just before the affiliate checks are issued."