So far, so good. One day, someone from this person's company registered on our site and posted a couple of spam messages full of keywords and links to this company's domain. Checking the user account, it did have that company's domain email (we validate registration emails), but the IP address was from a country very far away from here. The post was removed, and the account was banned per our rules.
I contacted the General Manager (GM) for that company and sure enough, there was an explanation: they had engaged a local SEO agency, and this agency outsourced some of the SEO work. Unknown to the GM the sub-contractor's link-building approach was "go around spamming comments and forums".
I told the GM that this was an unacceptable practice and that he was wasting money with that agency. Even more so because his domain name was so clear and related to their business that I considered that a waste of money.
His company didn't last long. The SEO agency is still around.