Any time you run a program where your affiliates rely on sending you visitors to make money, you will eventually have a problem with spam. One of your affiliates will inevitably get it into their head to blast the web with unwanted garbage. When this happens you need to be ready to take action. Otherwise, it will cost you! Your website hosting company can boot you off your server and you can find yourself blacklisted. If you get an email from someone claiming they received spam with your URL, then take it as an early warning. I am not advising you to immediately terminate the affiliate’s account, but be sure to contact them to follow up on the complaint. Let your affiliate know you received a complaint and advise them to remove this person from their list immediately.
If you only get one or two complaints, it’s probably not spam. The complainants might simply have signed up for an email list and forgotten all about it. You will know when one of your affiliates is spamming, because you will get anywhere from 10 to 100 complaints in the same day all regarding the same URL. The best thing to do in this case is to immediately terminate or disable the account of the affiliate URL that has spammed.