"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.