I was surfing the net when I came across this site called Website Looker. It is a "value calculator tool" that provides you instantly the estimated value of your blog or website. Aside from the general website report, Website Looker also provides information on your server, traffic rank, reach, page views, page views/user, bounce, time on site and search engine. It also shows your earning per day.
With this tool, you can verify your friends's blogs and website and how much their average earning. Try it!