I think that if the bribe has a contract attached, written or verbal, (which seems to be the current supreme court test for corruption here in America), then th

I think that if the bribe has a contract attached, written or verbal, (which seems to be the current supreme court test for corruption here in America), then the valuation would be the fair market value, or, conversely, be a pre-payment for services not yet delivered so the income wouldn't be realized on the politician's end until time passes in their term of office. From the briber's perspective, they'd have the asset of debt on unrealized income for services not yet rendered, and like all debt, that has a simple value (and if the politician becomes honest, then the debt is written off like all other debts you'll be unlikely to collect).