but how detect when price low or hight? Yes seller say me like this "50 000 visitors/month 2 000 $ profit" = price 100 000$If you want to buy full page then you can easy check monetizing of that page.
Ask for traffic and check rank
Check out this blog post: http://feinternational.com/blog/how-do-you-value-an-online-business/
Was written by a member of my team but is very detailed and should help.