Hmm it can do yes, the odd one you might get away with! If you have loads of pages then I would suggest not having any at all Kind of worrying question from someone who sells seo services!!
Yes. Dublicate content is bad for SEO. Iv got this problem, even thought i only have one page! The reason for it is beyond me lol!
im asking it because I have put meta tags in the header of blog so of course it will go in all the pages
let me tell you the better way to find and remove the duplicate meta descriptions. Go to web master tools and open html suggestions tab and you can find how many duplicate meta descriptions you have out there .. remove them all because they are harmful for your website specially after Google Panda
Ofcouse having duplicate content, meta titles and meta descriptions can hurt your search engines placement and rankings, if you use Google's webmasters then you can check if your contact is doing his work correctly.