It is important to document cases like these, so others in the future won't panic when such SEO blackmail happens.
The closest form I could find to report this to Google is: https://www.google.com/webmasters/tools/paidlinks Though not regular selling links for money, I would make note about that in the additional details and provide a link to their XRumer domain list.
The closest form I could find to report this to Google is: https://www.google.com/webmasters/tools/paidlinks Though not regular selling links for money, I would make note about that in the additional details and provide a link to their XRumer domain list.
In my experience the folks over at the webmaster forums: https://productforums.google.com/forum/#!forum/webmasters are good at, and interested in, handling these sorts of cases.