Positive ratings are heavily dependent on getting all visible dirt, debris, and smudges off of the floor. A vacuum that has good suction can really help. For a bagless vacuum, make sure to empty the canister after each apartment and check the filter for clogs after each day of cleaning. For a bag vacuum, make sure you're trading out the bag before it gets completely full as it has less and less suction as the bag fills up.
You can find a full overview of what the Neighbor (customer) expects from a standard cleaning here: http://bit.ly/lapa-lopa-cleaning-whats-included