It takes a good bit of persuasion and bargaining to convince a servant of the divine to grant a measure of holy power. Acting in service of their would-be patron is the most frequently-used bargaining chip, but there are other means of paying what is owed. It all depends on who you're talking to.
There's no tricking or deceiving them, because they always know if they've been lied to. Nobody has yet managed to outsmart the divine, but there will always be someone to try.