How do Search Engines evaluate that content is Good or Bad?

there are many factors - non-restricted - ..
the following are the most important adopted by search engines..google as an example: -the first & most important is : Content !! remember this: ConTeNT == King !! -Domain :Must be related to the contents !! -URL:yneed to use your keywords in the URL posts -H1, h2, h3...
headers -Keyword in first and last phrase -Meta description -Keyword density -Keywords meta tag -Length of the text -Alt-image tag -Bold, italic and underlined for keywords if does my answer help you, ihope you vote up :) good look :)

The search engines will observe how long a user stays on your site, the number of clicks, inbound links and the social media footprint pointing back to the website.

These are some of the factors: - Originality of content - Amount of content - Headlines and keywords used inside content - Quality of page coding - Users engagement (Do visitors spend time reading or "bounce" away quickly?) - Internet Assessors (Google use real local people in each country through third parties to evaluate search results and page contents)

SEO changes every couple months or weeks depending on what the Search Engines are trying fight against, whether it be SPAM or down and dirty content farms that aren't relevant to any one subject or niche.
Either way the SEOer is at the mercy of the Search Engines, and the White Hatters get caught in the cross fire of Search Engines and Black/Gray Hat SEOers.
So, how do search engines evaluate whether content is relevant enough to include in their SERP's? Well, based on recent Penguin and Panda updates done over the past 2 years by Google some SEOs say you don't need SEO, just great content (Although internal SEO is more important than external).
According to Matt Cuts, Google's head of the Web SPAM team, Cutts dispels the idea that sites that don't validate well will be dinged by Google despite good content.
"Just because somebody dots every i and crosses every t and gets all their HTML structure right, doesn't mean that it's good content." Source: Brockmeier, J.
(2011, December 13).
ReadWrite – Google's Matt Cutts: Good Content Trumps SEO.
ReadWrite – Web Apps, Web Technology Trends, Social Networking and Social Media.
Retrieved December 17, 2012, from http://readwrite.com/2011/12/13/googles-matt-cutts-good-conten So, coming from the horses mouth Google is trying to move away from SEO, and focus purely on content, even though great backlinks, author rank, authority and social media are becoming the other future deciding factors in Google's algorithms.
If you want to go farther down the rabbit hole there are a combination of content strategies that can get your company at the top of the SERPs.
A few examples are guest posts on related websites, the company website blog that internally links to other articles on the site and what I like to call content Islands.
Content islands are a combination of different content pieces that you distribute on the web, basically piggy-backing on the authority and rank of other content based websites that Google trusts and spiders on a daily basis.
Sites like: Squidoo & Hubpages (Google still ranks you based on good content produced on these sites) Buying up expired domains with PR and authority, then using them to write content on because you own them henceforth speeding up the content ranking process PDF aggregator websites Content doesn't only include written, it can also be done with video and rich media photos.
Like before this only scratches the surface of online marketing and content strategy.
Have fun, Phillip MacDonald Digital Marketing lover, SEO, Competition analyzer and marketing strategizer LinkedIn: (URL removed due to policy violation. Please contact support for further information.)

Google evaluating your content by the quality score which is mean every time somebody searching on Google and entering your website and navigate and find what they want your quality score for that keyword will grow