In addition to monitoring ad positions and quality scores, do periodical spot checks on the affiliate network's offer page, landers and the merchant sales page. These can often change without notice, or simply be forgotten about.
For example, link rot is fairly common. An offer may be pulled, but being busy at the time, you forgot to change the link on your lander, or redirect file. This results in frustrated users and blows any confidence the consumer had in your website.
(One of my friends had broken links for over a year, but being sloppy and lazy in his tracking, didn't notice. He only found out when I pointed it out. I can only imagine how much money he lost during that time, paying for clicks that went nowhere.)
Another issue is merchants that modify the conditions of the original offer on the affiliate network. The affiliate network is supposed to notify affiliates of those changes, but sometimes they don't. It doesn't happen that often, but often enough that the offer on the affiliate network needs to be checked weekly.
Also be sure to check the merchant sales page for changes. It's happened a few times, where the merchant sales page was swapped out, for a new product, which I didn't get commission on. The affiliate network was not informed of these changes. The only way the affiliate network found out is because I complained.
Don’t find customers for your product. Find products for your customers.