Nothing is ever really free. There is always some kind of exchange going on. For example, you don’t pay for the information you find on this site, but I subject you to advertising. You pay for the content by giving up a few mental cpu cycles. It’s no big deal because they’re mostly cycles you weren’t really using anyway. I’m not hiding anything either. It’s all right up front, and if you really object, you can use an adblocker and still read for free.
Many web sites aren’t so nice. In Why You Should Never Search For Free WordPress Themes, Siobhan McKeown gives a very good demonstration of the ways that some people trick you into paying for their supposedly “free” services. She googled “Free WordPress themes” and evaluated the first ten hits. Nine of the top ten sites were giving away themes loaded with trojan ads or worse. Only one site was giving away free themes that aren’t trying to hack your WordPress site: WordPress.org.
We always hope that we get what we pay for. Unfortunately, sometimes we do. Even worse, sometimes we get what we don’t pay for.