Who are the advertisers?
An ad network’s website will boast of its biggest advertisers but the bigger the marketing budget, the more agencies are going to spread it around. A big brand at an advertising agency then might not mean very much — giant corporations are as confused about the most effective channels as publishers are. What you want to know is whether you’re going to get advertisers who will appeal to your audience. The site — or the site’s agent — might give you an idea but you won’t know for sure until the ads are up.
3.What control do you have over the ads?
Unless you have a very large site, it’s unlikely that you’ll be able to choose your advertisers but you should be able to block ads placed by competitors and ensure that you’re not showing content that isn’t appropriate to your audience. Just about all networks should have some kind of filtering function in place, so you can safely steer clear of anything that doesn’t provide that option. And you’ll also want a way to place alternate ads in case the inventory doesn’t match your sites. Google provides this, and AdMobs can serve AdSense if it doesn’t have enough ads.
4. What is the fill rate?
AdSense is largely a CPC network but other services provide both CPC ads and CPM ads. In terms of actual revenue, there may be little difference but you should know what you’re receiving, and how likely you are to receive it.
5. Does the network suit your site?
That’s a very broad question, and one that covers whether the network reaches your geographical area, whether it serves sites like yours (some networks only work with the largest publishers) and whether it shows image ads, text only, search ads or ads of every kind.