google SERP problem

hi,

i am having a site which is showing 4th position when we search on google,

But when we use any serp checking tool, it shows 7th position or 8th position

Which one to trust ??

please suggest

example tool i used for my site : http://www.seoserp.com/web_tools/google_top_1000_serps_checker.asp

please help out

 

The 4th position is due to Personalized Web Search.

 

means ? didnt got you