I think more people should put some effort into curtailing their own comment sections. I know this is something that is often forgotten about. Even when a spammer is not flagged if his comment is somewhere near the bottom and to never be seen again then they might have to rethink things.
Granted some of them also just leave a comment on top comment to try and get some attention that way. I do tend to agree with kyriacos and only way is flagging them. If they are bot then they might not notice the rep drop for quite some time and keep spamming away so that just helps others notice. Other times it draws them out as they get angry over the flag and you might get a conversation with them.
Part of it is a culture thing depending on what country they live in that might be how they act there to sell a product or service. Another could be a language barrier. They just don’t speak enough English and they live in a country where $1 is all they need and someone told them about this “wonderful moneymaking opportunity” so they think they will get rich. When the site is sold to others in a way as a place to make money just by writing people just assume they can get rich and therefore spam.
I wish educating them was the way to go. I’ve written a blog or two on the subject matter myself in the past trying to show how to go about leaving comments and the benefits of leaving good thoughtful ones. I even spent some time leaving thoughtful comments to their spam or even ones poking fun at the comment. Whatever I could to try and get the person to reply back so I could have a civil conversation with them. Never had any long-lasting results as a day or two later they just go back to spamming.
I’ve seen a few well know people in the community try and address this issues without going on massive downvoting sessions to deal with it. They never seem to work. One even went as far as making a contest and rewards if you took the time to convince a spammer to stop and they went at least a week without doing so. Didn’t work out so well.
Actively curating our own comment sections. Take the damn time! Show-- by example-- how a good and engaging comment is rewarded and results in actual dialogue... give a small upvote to someone who's obviously trying but not good at English. Give a tiny upvote to someone who at least show they READ the post. FLAG the stuff you can readily identify as spam... it orders the comments meaningfully.
And curate good comments elsewhere! If someone wrote a stellar comment on someone else's post, give 'em a nudge; dropping a few 10-20% upvotes on comments isn't going to kill your voting power.
Our words matter. And downvoting does need to be used for appropriate spam.
But some folks are just not good with words or communicating. I take the time to notice if they are saying "good post" versus "look at me".