We've got a new member today 'Dan' who seems to be bent on promoting his own product 'Sizester'. His first question was more of an advert and he's supplied two answers that both promote his product. I've no idea what the correct process is for dealing with this sort of problem though so I've edited out the name for now but the whole thing is probably worth a review.
The site FAQ has a section that's relevant: https://photo.stackexchange.com/faq#promotion
People who are first attracted to the site by the desire to recommend their own product can become helpful and productive community members. They're often experts in the domain of their product, and that's useful to have around.
Responding with a pointer to the FAQ and suggesting an edit is a good start.
If the answer is useful with the product name and links removed, making that edit could be useful, but in many cases that just leaves a meaningless comment. In that case, asking the poster to expand and justify the answer seems reasonable — and downvote until that happens. If it doesn't get a response in a few days, it was probably just a "drive by" by someone with no real interest in participating. In that case, the post should be flagged for deletion.