I have comments enabled on my blogs, but they are moderated. That means I have to approve them before they are published. I haven't put in place lots of hurdles for people to leap over (when I'm faced with a capcha code, followed by the need to register, followed by the need to log in, I tend to just give up at some point).
But it's just as well I have moderation in place because of the occasional spam comments I receive.
What is a spam comment?
I regard as spam any comment that is irrelevant to the post being commented upon. Even apparently nice comments fall into the net.
For example, if someone writes: "Great post, really interesting" followed by a link to their blog, my sense is that they've only commented in order to gain publicity for themselves. Maybe they read somewhere that you're supposed to comment on other people's blogs for that reason, but I don't think it's too much to ask for some useful feedback.
In this example, if the comment says why the article was useful, then I am more likely to believe that the comment was neither a cynical attempt to piggy-back onto my blog, nor written by a bot.
Otherwise, my usual response is to delete the comment unless I know the person who wrote it.
Comments with links to completely irrelevant products are, of course, spam. But even links to ed tech products are, in my view, spam if there is no obvious reason to include the reference to them.
For example, if I leave a comment on a flipped classroom article, and then throw in the fact that I run courses on assessing Computing, that ought to be seen as spam -- unless I can show a link between the article and my courses.
When I receive comments that seem to be nothing more than a vehicle for advertsing, I delete the comment -- and report it as spam. That ensures that comments from that IP address don't appear again, I think.
A real life example
I recently received a complimentary comment that contained a link to a website that provides essay-writing services for students. That kind of site had nothing to do with the article being commented upon. But even if it had, I will never knowingly give publicity to such websites or services. Therefore I deleted the comment and reported it as spam.
This rushing for the Delete button may seem a bit harsh. Why not engage in a conversation with spam commenters?
First, if the comment was written by a bot, there's no point.
Secondly, spam commenters invariably leave no contact details, making it imnpossible to contact them anyway.
Third, I tend to not engage in discussion with spammers or trolls, as a matter of principle.