Well think about user intent. You're attracting a bunch of people who are looking for free stuff, so they're not really optimized to click on ads. They want FREE stuff. I have some sites like that too - I have AdSense on them, but I don't expect too much because I'm not catching them in a buying cycle. The best way to deal with that is 1) work out a way to push them into buy mode, or else 2) get a bunch more traffic. The first is more likely to succeed than the second. Best idea is to do both.