I'd really like to have a place where we can report those dubious "SEO companies" who are sending spam e-mails to website owners offering to write "guest posts"

I'd really like to have a place where we can report those dubious "SEO companies" who are sending spam e-mails to website owners offering to write "guest posts", so they and their practices can be scrutinized better by the community and perhaps search engines. For example, slap-up-media.net spammed us today, offering to pay us to publish guest posts written by them. I'd really like to know who their clients are (but would not risk accepting their offer out of curiosity).