Using Seo quake you can check the quality of backlinks. To know how many outgoing links are present on the site, pr of that sits, total no of links present on the site. Also, use nodofollow firefox extension for checking dofollow and nodofollow.
Well things you have to check out are 1. Are the links nofollowed 2. What is the pr of the linking page? 3. Does the page have too many outbound links? ( since pr is divided) 4. Is the linking page blocked by nofollow 5. Is the website which is linking relevant?( similar of same theme) 6. Is the website penalized ( or doesn'nt appear in the SERPS) 7. What is the traffic of that website?
also you can use yahoo site explorer to check competitor backlinks...and foxyrank is a great plugin to check for nofollows without going through the code
yahoo and google have a tool to check backlinks, just type in "link:www.yousite.com" in the search bar.
I am agree with visualskirmish bse its a very easy and good method for getting a true result of site backlink.
How do I assess quality of backlinks: - page in robots.txt? - page has <meta robots noindex>? - link has rel=nofollow? - link is after </body> or </html>? - is the page indexed/cached by Google? - page PR - site PR - number of OBLs on a page - Alexa rank of a site - number of Yahoo backlinks for a site - domain registration year - is the site relevant to your niche? - how many clicks to reach the page from the main page? - originality of a content on the page - ranking of the page in SERP by its main keywords Manual work would kill you here. Only pro software can give you the result. P.S. Implemented all these checks in our system.