They appear to surface most in the recommendation threads. Is there anything that could or should be done about them? (I mean, their answers may be perfectly valid, I don't know.)
If the poster identifies their connection with the recommended product, and the recommendation is a possible solution, then it's usually OK. Else, downvote it and/or flag it as spam.
Also check if the user in question has a pattern of providing the same response near-verbatim (as is the case with the former), then it is likely spam unless it meets the criteria indicated above.
Generally what we are looking for is
The answer, as with any answer, should be on-topic and a legitimate answer to the question -- absolutely!
The poster should have at least a little history of providing answers other than links to this product or service. We need evidence that this poster is someone who participates in our community in good faith, not just to astroturf.
(also, if this is a "drive by user" who made that single post and never came back, it's probably spam.)
May I promote products or websites I am affiliated with here?
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 they happen to be about your product or website, so be it. However, you must disclose your affiliation in your answers. Also, if a huge percentage of your posts include a mention of your product or website, you're probably here for the wrong reasons. Our advertising rates are quite reasonable; contact our ad sales team for details. We also offer free vote-based advertising for open source projects.