I took a closer look at the deleted answer and it doesn't really appear to be spam.
Belarc Advisor, the utility linked in the answer, is in fact a legitimate program. The post was nonetheless deleted for low quality because it contained no meaningful content beyond the link to download the software; however, a mere link is not sufficient for a post to constitute spam.
In the future, the best thing to do is probably to downvote answers like this. If it warrants deletion, flag as "very low quality" or use a custom moderator flag explaining the issue (but note that I've gotten inconsistent results with such flags).