When Google started heavily rolling out personalization, people started writing articles that it was the end of SEO (Search Engine Optimization). There’s even a new book on it, The Filter Bubble.
How can you optimize a site when everyone is seeing different results?
What do rankings even mean in such a world?
Of course that was vastly overblown. There is only one situation where Google serves up vastly different results: If it looks like you are searching for something local.
In that case, even if you don’t include a location in your search phrase, Google will assume it and serve up results at least partially based on your location.
Search for “plumber” and chances are you’re looking for someone nearby (though you might just want to know what a plumber does or be looking for a photo of one). That presents no issues for optimization at all, if you are optimizing a local plumber’s website.
There are some other differences for sure. For example, In your usual browser, and especially if you are logged into a Google account, your own website is likely to show artificially high in searches. Google knows you’re more likely to click onto your own site.
But mostly the differences are rather small, one or two differences in rank depending on who or where you are.
Google’s Chairman, Eric Schmidt made the same point recently:

“The differences are pretty small, he said, saying the personalization aspects are a small component of the rankings. “I think that’s a little bit of an overstatement to make a point,” he said.

(Quoted in this article.)