I’ll often be asked about “good places to find free WordPress themes” and the only places I’ve come to recommend are the official WordPress Free Themes Directory and more recently the Free Themes area of ThemeGarden. WordPress is a fantastic piece of software, spammers love taking advantage of fantastic software. WordPress has an entire market of spam-filled assets out there, and it’s a professional responsibility to educate others about it.
Like anything, if it’s too good to be true, it probably is. Many SEO’d free theme sites are just that, as this article points out. Give it a read as a refresher, and if you run your own WordPress site or are asked for help about free themes, make sure you’re giving good advice.