A user recently posted a question that asks, "How do you do X?" In the user's profile, there is a link to a software company that makes a paid-subscription product for doing X.
The user isn't explicitly shilling (or even mentioning) their product in the question, but it seems that they're only asking because of the services they provide - not because they, themselves, are trying to figure out how to do X. While I understand that people selling things like to do research about those things, it seems a little disingenuous to use a Q&A help site aimed at helping people who have real problems to do that research, especially without disclosing to the people providing answers that you're using them for researching your product.
This doesn't seem to be covered in the site tour or site help that I can find. I did some searching here on Meta and found one question asking about people posting answers related to products they're involved in, but I can't find any guidelines about questions related to products where the user has a commercial interest.