To put it succinctly:

This is not something that professional system administrators do. While we certainly might evaluate the reputation of a domain registrar, obtaining a registrar's customer list is not part of that process, because it's usually impossible anyway and because it wouldn't provide any useful intelligence that couldn't be found via other, more public (and more ethical!) means.

If you're truly curious, you may find that this question gets a better reception at our sister site, [Webmasters](http://webmasters.stackexchange.com/).