@denmarkguy the solution is simple. Follow what instagram has done to check this. If you try and copy paste a comment 3 times or so, A pop-up appears and tells the user something like "youve typed this before" dont remember the exact words. So this kind of forces the spammer to change his comment after every 3 posts, otherwise the comment doesnt go through. This applies only when commenting on other peoples posts. If you are replying with a "Thank You :)" as a reply to your own posts comments received, instagram makes an exception. You can post Thank You as many times. Maybe SteemIt needs some AI