What is the test for determining whether an individual who overpaid by mistake is to be found at fault for overpayments?

The regulations provide that an overpaid individual may be found at fault if the overpayments resulted from: (1) an incorrect statement made by the individual that he knew or should have known to be incorrect; (2) failure to furnish information that he knew or should have known to be material; or (3) acceptance of a payment that he either knew or could have been expected to know was incorrect. See 20 C.F.R. S 404.507. The overpaid individual bears the burden of proving that he was without fault. See Anderson v. Sullivan, 914 F.2d 1121, 1122 (9th Cir. 1990).