Ya meen he flip-flops too? So that's who Kerry got his talking points from.
Actually, I got that line from the 80s Robin Hood BBC series, which my wife is a fan of. friar Tuck says it while they're dealing with a cult of devil worshippers who are ravaging the nearby villages.
I'd presume that the Devil can't make a binding contract because he is by definition unable to agree in good faith, no pun intended.