Applicants who state they are not married when they are. Those receiving Supplemental Security Income (SSI) can have their benefits reduced by their spouse's income and assets, so some applicants may wish to hide the existence, income, or assets of their spouse.
Claims of blindness. In particular, the Social Security Administration is concerned about those who declare they are blind and unable to drive, but are later found to be in possession of a driver's license and are observed (legally) operating a motor vehicle.
Unreported income. Some types of income that often go unreported are from renting out a portion of one's home, or from an insurance policy.
Employment changes, in a person who was not working at the time they applied for and started to receive benefits, but has since returned to work.
A person who is the legal custodian (representative payee) of a disabled person's money spending it on some expense other than that of the disabled person.
A person who cashes the checks of a deceased person.