Besides click fraud, some examples of affiliate fraud include:
Placing a variety of cookies on a visitor's browser (cookie stuffing) to raise the chance of earning a commission when the customer decides to make a purchase in the end.
Creating fake IP addresses (IP spoofing) and secretly clicking links on their site to artificially generate traffic from their site to the merchant's portal.
Using VPNs or proxies to make it appear that a sale was secured in a different country when they've actually made the purchase themselves.
Entering the numbers of lost or stolen credit cards to make a transaction on the vendor’s website.