As I've indicated upthread, I don't regard it as a pact.I find that there is an unavoidable conflict of interest when one party decides his PC will adhere to a code of subservience/adherence to another being or ethical philosophy- as in a cleric or paladin to his faith & code- in exchange for powers within the campaign world AND is given the ability to adjudicate whether his PC has successfully met the terms of that pact.
Also, I don't run a game in which the players get any advantage by violating their code. For instance, the game doesn't become more fun, or the players field of action (via his/he PC) become any larger, by violating the code. (This is not true in all D&D styles. For instance, it is not true in Gygaxian "skilled" play. But I don't run a Gygaxian game.)
Hence, there is no conflict of interest in my game.
The situation is in my view not really comparable. You have powers that you could abuse, and a standing temptation to steal from the client trust account.I am subject to an externally imposed ethical code as a condition of being granted all kinds of powers.
But as I already noted, the player has no advantage to gain by having his/her PC break the code. (At least, not in the sort of game that I run.)