It always tickles me that:
A) people assume the much touted independant and free-spirited Inquisitors have superiors because (the very entertaining but canonically unsound) Dan Abnett made it seem to be the case in his series of books.
B) people believe agents with absolute power in a fuedal system have to pay for services.
It is the duty of all individuals in the Imperium to provide whatever services they might be called upon to perform to the Imperial authorities, it is both criminal and heretical to refuse.
As such the only way to legally refuse an Inqisitor's request for an item is to claim (truthfully or not) to be incapable of providing it for some reason.