How accurate is average position for search queries in google Webmaster Tools?

[bucz]

I asked myself that question and decided to check it. It shows that for 'wedding photographers Glasgow' I'm on 22 position. Great! I think to myself. Then I googled this keyword in an incognito window. Went to page 3 and I'm not there. Clicked next one but nothing there. Finally found myself on page 10!
Is this appropriate way of checking the actual position for certain keyword? Why is Webmaster Tools showing me on 22 position? I mean it's not even close to the actual score.

 

[nass]

Check out https://moz.com/ugc/testing-the-acc...-for-search-queries-in-google-webmaster-tools

and fyi: #97 for me