"We can do better than AdSense" is a very common selling point for alternative ad brokers. In theory, somebody should be able to do better than AdSense. However, I haven't found an alternative for ads on my site that works better than AdSense.
When you get these offers you should:
- Research the company. Look for online reviews and if other folks have had success with them.
- Test their ads on 10% your site. Ideally random pages from your site or alternate over time between Google AdSense. You want to be able to compare revenue in an A/B test.
- If they do better than Google, use them more. Keep Google running at 10% at least for a few months, just so you can continue to compare.
At the very least, it is always a good idea to have another ad network lined up ready to go or running minimally. What if your AdSense revenue tanks? What if AdSense closes your account? It happens.
If you use an Ad Manager on your site such as Google DFP, it makes it very easy to set up ad tests. You don't have to program anything or swap our JavaScript snippets. You just enter their JS into the ad manager, and set up rules for how often they show up.