I believe many newbies do use the wrong tag for some posts simply because they want to use all 5 tags and they don't quite know where it fits outside of its main context/content. I myself have done so, once, and was informed with a reply.
I believe that replying to the post is a good first step. Guidance is certainly better than reprimand and it offers those Steemians that are making honest mistakes the opportunity to learn and grow in the community.
I,m sure there are people on Steemit who abuse tags constantly using only the most popular tags to gain viewers. Those people should be dealt some sort of punishment. Many Steemians, myself included, don't want to use their power to reprimand and take away from people who deserve to be noticed.
Maybe you could try a 'black-ball' system. Create an image or .gif that you could reply to these people and let the word out on Steemit that any post that has that symbol in their comments should NOT be upvoted. Or something like that. Kind of a scarlet letter thing. Maybe. Or maybe I'm just crazy.