Yes, I've seen that ad. If you google Publish America, you get all sorts of warnings about them, such as this:
http://www.steelypips.org/miscellany/publishamerica.html
plus the writesr Beware site, and preitors and editors. In Britain there seems to be fewer such preiditors, but also fewer warnings. I fear that many beginners fall for them.
I found this thread when I did a search for Publish Britannica.