Entry About Itself

What does that mean?

I'm getting a few "comments" that are obviously marketing tools. I spend quite a bit if my blogger time deleting them. I like anyone really appreciates a visitor with a comment, but not adds like "I was reading your blog and it's great. I have a site you might be interested in" yea sure, I'm really interested, I'll go there right away! Any tips on how to avoid this? Anyone else experiencing it?