Among the list of criteria Google uses to display the most relevant search results to users, your personal data are definitely used. That’s fact!
Let’s see how we can figure it out :
Here is the result of a search request with keywords “Java Hoster”. The website Java-Hoster is then ranked as 4th result.
Java-Hoster is only ranked 6 !!!
Then it clearly appears that somehow there is something stored in your Google account containing something related to pages you’ve visited, even if you toggle off the Google history feature.
In addition to that, Google puts forward the results you stared : not only on the stared section, but more generally they appear better ranked than if they weren’t.
That is also why whenever you have access to reports containing you rankings concerning your website, you may spot some discrepancies. It is then very difficult to compare results and to have a clear vision of you ranking since it also depends on user.