Been noticing some proxy listing sites filling up with these fake proxies on domains from freedns.afraid.org.
This is one here for example
service.opinionatedmag.com
There just stuffed with Adsense and a embedproxies.com form. There is no proxy service being offered on the domain/server.
If you own a proxy listing site. Make sure to check its a real proxy before approving it.

Is there a script that automatically checks all listings to see if they are genuine proxies?

You could put a function into the script to check that its not on a subdomain.