Spam! There is no single accepted definition, but I think most bloggers will agree, spam is unwanted commercially motivated electronic communication (not limited to email), that’s a likely a source of malware.
I think most bloggers will also agree on what isn’t spam. No commenter should be shut out of discussion on your blog because you disagreed with their point of view and inappropriately marked their comment as spam.
Dealing With Spam
Spam affects everyone involved with the Internet including, among others, network operators, ISPs, businesses, recipients and, at the most basic level, the infrastructure itself through burden that it places on the system. For that reason, fighting spam requires a multi-stakeholder approach. — Combating Spam: Policy, Technical and Industry Approaches (PDF)
Over 80% of all so-called comments submitted to free hosted WordPress.com blogs every day is spam and we WordPress.com bloggers have Akismet, an excellent spam filter.
If you get spam that slips by Akismet then mark it as spam (do not delete it) and over time Akismet will learn it’s spam.
On the spam that Akismet sequesters it takes only seconds to click “empty spam” and you don’t even have to click “empty spam” if you don’t want to. Akismet will maintain comments it has caught for 15 days from the date of receipt and will delete the comment automatically.
Read more here > 5 things every blogger should know about spam
Develop a Commenting Policy for Your Blog
Freedom of speech comes with responsibilities. Develop and publish your own commenting policy. Then when a commenter does not parrot your own point of view back to you or states something you disagree with suck it up ie. deal with the comment appropriately.
In Blog Comment Policy Lee Odden five criteria for a comment policy include Comments are welcome and encouraged; Comments should add value; Keywords in the “name” field are spam; Links must be relevant, No signature [links] in blog comments.
Mark Spam as Spam
Sooner or later you will receive a dodgy commercially motivated comment that slips through the Akismet spam filter and you will have to mark spam as spam. It may be either bot generated or human generated spam. It may or may not have a keywords in the “name” field. It may amount to a shameless self promoting plug in very poor English, or it may contain insincere flattery. It may or may not or be full of links to bad neighborhoods, etc.
Mark only spam as spam
Bottom line: If you are not secure and mature enough to pacify your inner control freak, who cannot tolerate criticism and longs to censor those who do not share your POV (point of view), then seek treatment for what ails you before becoming a blogger.
If you do blog then sooner or later you will receive a negative comment that does not violate your comment policy and it’s best to have a personal policy in place to deal with that too. Approve the comment and refute the contents or thank the commenter for sharing their point of view and blog on. But, don’t pollute the spam filter with false information by marking comments you don’t like as spam. Mark only spam as spam.