31 CFR § 29.523 - Equity and good conscience.
Recovery is against equity and good conscience when there is substantial evidence that—
(a) It would cause financial hardship to the person from whom it is sought no matter what the amount and length of the proposed installment;
(b) The recipient of the overpayment can show (regardless of his or her financial circumstances) that due to the notice that such payment would be made or because of the incorrect payment he or she either has relinquished a valuable right or has changed positions for the worse; or
(c) Recovery would be unconscionable under the circumstances.