A willing buyer and a willing seller are needed for a valid contract but there’s no possble contract for crime. One area of prostitution law is where both parties expect to be satisfied, one with payment and the other with satisfaction.. Sexual satisfaction however takes different forms. We cannot have men going around selling movie appearances for sex, ….. but, … agreeing to sex for a movie part is a sort of understandable bargain. So is the more common situation of selling sex for a movie part. If a movie part is sold for cash, … I’ll pay you to get me in a movie, … it’s a simple contract. If the cash is paid back for sex, … I’ll pay you cash for sex, … it’s an offer for prostitution… and the parties would simply not exchange the cash, just go from promise for a part to actual sex as payment…. A Quid Pro Quo… Or a Pro Pro Quid… Two payments for two things..