Thank you but no thank you

I have gotten a couple of comments with: 'Beautiful blog.' And then another comment followed that at the same instance (I get the email alerts at the same time): 'Please read my post.'  I've seen other bloggers getting the same comments and they left them published and I did the same thing. Then a few months after I got those, I get them again (they come in pairs or triplets with a repetition of one or the other comment) and again, I let them go. Then for about a couple of months, no more of those comments and then they came again just last month - I just couldn't stand them so I marked them as spam.
    As a blogger, I don't think you should beg people to visit you which these messages seemed to say but perhaps other people have a different interpretation. I didn't visit this person because I just didn't feel right to do so. And I couldn't decide if they are spam or not. Why do they leave the same three comments with the same wording over and over? You could say it's because of language constraint but that still didn't explain the repetition. Getting these same comments over and over seemed like spam so why should I respond to them or visit them when they might turn out to be spam?
    Then there's these comments that are weirdly worded, gave no clue as what they are trying to say, like they are quoting song lyrics or talked as if they belonged to a different century or planet and they didn't seem like real comments even if they did use my name. No idea what was the point of these comments. Besides that, they get marked as spam by Blogger so I left it.
    Then there are those one-word comments. I think if you cannot think of at least three words to say, just don't do it. Actually, it is just better not to leave a one-word comment because they'll be marked as spam by Blogger but I got sick of marking them as not spam so I sometimes left it.
    And then there were a few bloggers who left generic but nice comments but they had commercial blogs/websites so I didn't return a comment. I don't believe readers have to return comments on commercial blogs or any blogs that didn't interest them.
    It shouldn't matter what readers say in their comments but I guess I'm a picky blogger but also Blogger somehow marked most the above comments as spam so if I don't check, they stay there in that little space until I delete them (which probably never happen because I loath to check that space.)  I like comments to make sense and that I don't have to decipher them or wonder if they are spam or not. Maybe there should be some rules for commenting? I don't know. There's no right or wrong way to leave a comment but common sense should to be something to consider, right?

If you're a blogger, do you think it's right to mark certain comments as spam even when you're not certain they should be?