The Zombie Stack Exchanges That Just Won't Die
Specifically inspired by this answer.
The wording of the answer, combined with the user listing the same URL as their website on their profile, makes this seem pretty obviously like self-promotion.
The FAQ sayeth:
Be careful, because the community frowns on overt self-promotion and tends to vote it down and flag it as spam. Post good, relevant answers, and if some (but not all) happen to be about your product or website, so be it. However, you must disclose your affiliation in your answers.
So, what's the way to deal with these kinds of questions? Comment, edit, or both? Or is a one-off promotional post on an appropriate question "harmless?"
John Flatness
Not "harmless", that's for sure. If we allow this to continue, it won't be long before there are companies that sell to libraries flooding answers strictly to advertise their brands.
Comment that self-promotion without a statement about being affiliated with the company is not appropriate for the site. Just like the FAQ says, "you must disclose your affiliation in your answers."
In that particular instance, based on both the answer & profile, that it is spam and should be flagged as such for a moderator to take care of.
As for promotion in general, I think it depends on the case. Mentioning a product you've used and have experience with and is relevant to answering the question is within the bounds of acceptable promotion. As you and KatieR quoted, promoting your own creation/business/etc without acknowledging your association is against the rules.