I declined the flag, and so these are my comments:
First, you should be aware (and might already know) that flags on Stack Exchange have non-obvious side effects. For instance, simply flagging something as spam will also give it a downvote, and having a "very low quality" flag marked as helpful will also give the flagged post a downvote. In the case of spam flags, there are a lot of non-obvious side effects, since data from these is fed into a variety of anti-spam systems.
Thus, moderators should not dismiss a flag as helpful simply because the user who flagged something was trying to be helpful.
In this case in particular, while the answer did appear to be a recommendation for a commercial product that would (in theory) solve the problem, the user did not appear to have any connection to the company. Nor was it a drive-by spamming; this user, while new to SF, has a long history across the network. These factors led me to believe that, while the answer could be improved, it didn't really qualify as spam.
What I'm looking for with spam flags is:
- Blatantly obvious garbage from new accounts (which is posted by bots or non-mechanical Turks in developing countries)
- Users who are going overboard promoting their own product or service. (Though in the case of maybe a single post, since disclosure is what's required, if it's that obvious you can simply edit in a disclosure.)
This one might have appeared to be one of the former, if you didn't look closely to see that the user had been around a while and had a history on the network. Believe it or not, moderators don't just click buttons randomly. :)