I have recently been involved in a thread
where it is patently clear that a one of the posters
was shilling for a software product without revealing the fact that he is an employee of the company that makes that program.
This issue is perhaps a bit different from the problems I have read that the forum is having with spam registrations, since in this case it is an actual human composing targeted responses that all point towards one solution (his company's products), and not a bot.
The forum rules
only state "no spamming," and I think that could bear an update to spell out what that means in greater detail. For example, I would suggest that failing to disclose a direct financial relationship with a company or product that a user recommends be grounds for banning, and that this disclosure must be made in every post that contains such an endorsement.