How many visitors a site has?

You are contacting a website for some business purposes like offering a partnership, or wanting to advertise on that site, etc... Of course the partnership is more interesting or advertisement will be more expensive if the site has a lot of visitors per day. So unless there is a counter on the website you cannot really know how many visitors a site has and if your contact tells you 10 000 visitors per day you can only believe him until you start to advertise and you see the impression report but then you already lost time and probably money. So how can you know if your contact gave you the right information? You cannot because those numbers belong to the owner of the site but... you can have an estimation.

Statbrain.com gives you an estimation of visitor per day. But as it is mentioned on the site it "estimates the number of visits that a website has based on offsite factors like backlinks, Alexa Rank etc. Statbrain does not have access to log files or any counter information. The number of visits that Statbrain estimates gives you an idea of the number of visits that a website has, but not the exact visitor number." Keep in mind, too that this is different from unique visitors. However, if you are told that there are 10 000 visitors per day and statbrain tells you 1000 you can guess that there is something wrong and you should make some further investigations before agreeing on a deal.