I think one of the reasons your not allowed to mention the name is because it in some way helps up its ranking on google searches or something like that and of course we don't want to help promote the site. I maybe slightly off the mark and my explanation wasn't great so hopefully a mod can explain in more detail.
I know a lot of members check the free ad sites regularly and have even managed to get help with seriously bad situations. Some purrs members even have "free ad cats" that have been saved.
JackSpratt actively tries to help free ad advertisers find suitable homes for their cats and has even campaign to get the advertising of animals bands on one of the free sites.
It is definitely very sad and worrying...especially the amount of unneutered female with ads highlighting that they could be used for breeding or just have one litter.
Sometimes it seems like all the hard work rescues and purrs members are doing is being cancelled about by some of the bad things that go on within the free ad sites