if your website links to another site that has been blacklisted by Google this is bad for your ranking
Sites like onlinealley helps you to know if there're problems with a website you are linking to.
Does any Google API Exist .. or how are websites like this checking if a url is banned?
Are they checking the 'PageRank value' or something else?
Thanks
I like the nofollow suggestion. Its what SO does. Take a look at the page source.
You could also maybe do a 'site:PLACE_URL_HERE' lookup on Google to see if it actually returns any pages.
Also have you looked at the Google Safe Browsing API? Looks like that might be what your after.