you can expect a background investigator to talk to all your neighbors and landlords. the references you list as well as any others they can identify. they will check for criminal and civil records in every jurisdiction where you have lived.  they will contact you schools and verify you education. the will check to see if you listed  all your past employment on the application.. if not they may disquilify you... any differences between what your report and what the investigator could result in your being disqualified.