Market research is a fundamental area of research that you should be doing on your competitors. Also, if you are buying a website then you should use the following market research tools to learn the hidden secrets of the websites:
SpyFu – Spyfu is a web scraping tool that will show you what a site spends on Pay Per Click adverts. This will tell you if a site is expensive to maintain.
URLtrends gather SEO data, Pgaerank, links, rank trends and more.
Backlink Checker See who is linking to a specific website.
Market Leap Test the rankings of web pages. Great for testing competitor’s sites.