For the purpose of documenting an expenditure as a deduction or credit under this chapter, absent clear and convincing evidence of fraud, a taxpayer's statement or invoice from a credit card company or other financial institution reflecting the expenditure shall conclusively establish that the expenditure was made by the taxpayer, and the taxpayer's sworn statement that the expenditure was made for an identified deductible purpose shall conclusively establish a taxpayer's right to a deduction or credit.
Idaho Code § 63-3042A