This is why you hire someone to appraise the value of the item and document the third-party appraisal. If someone else says your painting was worth $20m on the

This is why you hire someone to appraise the value of the item and document the third-party appraisal. If someone else says your painting was worth $20m on the day you donated it, and they're wrong in the view of the IRS, well, it's an honest mistake on your part and at worst you just have to pay some money for getting caught.