I run CPM ads on one of my informational, non-transactional sites, and would like to sell that ad space directly to advertisers instead of sharing revenue with a middle man. I've had some offers from people wanting to run banner ads for items like health supplements. I've turned them down because my understanding from a few years ago was that even being associated with health supplements (or gambling) could get you in trouble with Google.
Today it dawned on me that I don't recall where I got that information, or whether it's remotely accurate. Maybe they were only talking about text links?
*A lot of the CPM ads I get are not for products in my niche, but they are of interest to my visitors. I don't consider "relevance" as important as "is this what my demographic is into", but Google seems to view things differently.