Previous Searches
Google will remember regularly searched similar keywords and offer results based on prior searches.
Previously Clicked Results
Pages visited from the links in the results Google returned will start to show up more frequently in results. Frequently moving higher on the page and occasionally creating a false impression of ranking higher. This factor can return competitor heavy results if a client has a habit of clicking on their competitor’s sites.
Geographic Location
Google relies heavily on location services, meaning that the search results will generally reflect the location settings on the device you are using. If you were to remove geo-modifiers and search in various locations you will get different results depending on the services offered.
Type of Device
For example, mobile users are more research-oriented, where desktop users are more likely to make a purchase. The varying intent was so strong that it prompted Google to roll out a mobile-first index. Meaning mobile search results update more regularly and the results vary significantly to the desktop counterparts.