It is very difficult to create a system where quid pro quo is eliminated. Strangely, it is a trust system now in order to avoid the appearance of quid pro quo. IMHO, the buying and selling of politicians is impossible to stop.
Even totalitarian states whose masters murder millions have corruption. No government of any form devised by man can be entirely free of it. It is why our Constitution only functions for a moral and religious people - because those are the only sorts who can hold corruption in check.