macd21 said:
It depends. While few people, even powerful ones, are going to know an Inquisitor personally, there are a number of well known, easily contactable Inquisitors out there. In particular the Lord Inquisitor of the sector. If an Inquisitor asks you to help him virus bomb a world, odds are you'll try to contact the Lord Inquisitor and ask his opinion on the matter.
Well, virus-bombing a world is pretty serious business. It's not like an inquisitor just pops up and demands an exterminatus. If the Lord Inquisitor is easily contactable, chances are, he will already know about what's happening and perhaps might be involved.
If he isn't contactable, then you'll just have to rely on the Inquisitor you've got.
macd21 said:
That's where personal contacts and allies come in useful. Having someone in, say, the Imperial Navy whom you can rely on to do as you ask is a huge asset. For all the authority the Inquisitors have, they still need to use the Adepta to get things done. And if the adepta aren't cooperative, you might as well hand in your badge, 'cause you'll spend more time making sure your minions are doing their jobs than hunting down heretics.
If the adepta aren't cooperative, then they are obstructing the inquisitor's holy duty and are heretics in the eyes of the Emperor. Disrespect for authority is literally a heresy punishable by death. Duty is the grease which keeps the wheels of the Imperium turning. If Inquisitors can't rely on someone to act on their command when it is needed, then the roots of heresy grow deep indeed.