Client side relevancy parameters
As a webmaster you do not have a great deal of control over these, apart from targeting successfully your audience.
Search tools tend to have the best possible relevancy regarding the users and their algorithm is using some of client side parameters to display the most relevant results.
Below we have a few of the client side parameters that are taken into consideration and can have an impact on the results displayed.
Once again lets start with the obvious. Google, Yahoo etc ... do not display the same results in the different language versions. It means that if you make the same request (even in English) in Google.com and Google.fr you won't see the same results.
In the image below you can see the difference between Google.com and Google.fr - In red the results which are the same (wikipedia). In green the results which are different. You can also check by yourself for .com and for .fr.
People should be reminded that the google bar uses google.com by default.
Google index is stored in a number of datacenters which are spread around the globe. Internet users are connected to one of these datacenters depending on their geographic location - determnied by their IP address.
If two requests are made to Google from two different places in the world (or even in the same city) you may not be connected to the same datacenter and will see different results.
Google also uses this technology to display the "Local results" of the sponsored listings.
Set up of your web browser - This is one parameter I have seen when working on international clients. One of them was always complaining about the results accuracy with our platform because the results he was seeing on his computer were different.
One day I was in the client's office (the client is Swedish - so was in Sweden) and we made the same request in Google.com. We both have the same IP adress - My browser was in English (UK) and his was in Swedish. And the results that were displayed were different just because of that.
Try this at home!