Comments should be relevant to the topic. Comments that are not relevant are considered spam. Well, you can check the identity of the commentator by a reverse lookup of their links. The email address will also appear in your email together with the IP address of the commentator and these are your bases in order to know if a particular comment is legit of not. The idea is they should be filtered in your comment section and set for approval of the owner of the blog before they will appear in the comment section. Another thing is that comments with so many links/URLs are not good.
If this is your standard in your blog, this should also be your attitude towards other blogs. You should comment on other blogs relevant to their topics and once your comment is approved and the owner of the blog has replied to your comment, you should also reply in order for him or her to know that you are interested with the topic and you are sincere with your commenting. In order to trace back where you have placed your comment, you should subscribe on the comment/article so that you will be updated on your email.
It is also good to place recent comments widget on your blog if it is possible. This is for the visitors to know how valuable your posts are and this is also for you to be able to respond back to the commentators. You should respond to real commentators and not spammers that is why as much as possible, if you can put a CAPTCHA on each comment section of your blog, it is good to place this one.
There are so many creative ways to maintain blog comments in your blog. If you can have the widget “Recent Comments” this is also good since we have to admit the fact that there are so many SEOs out there who would like to belong to the top commentator’s list for SEO’s sake.