This question comes from a little trend that I have found on this forum, the constant questioning and complaining around looting and how the acolytes always are "misusing" it, taking anything there isn´t nailed down with them, just to sell it in the next town so they can get some better gear.
One thing that I often wonder when I read that is why GMs even allow their players to loot in most cases. Think on it, if they loot anything from a loyal human (here coming to mind The Adeptus Arbites, The Admini stratum, The Adeptus Ministorum and all the other nice imperial cults) is it theft. Just because the owner are dead does it not stop being owned by the imperium, a lasgun is still the guards lasgun even if the soldier is dead, a sacred tome is still the church tome even if you have burned the building down and killed all the priests, that pair of handcuffs there is sitting around yours wrists are still the Arbiters even if you manage to run to the other end of the universe with them in your backpack.
So that deals with that, you can´t really use "loyal" equipment as loot, sure you can use it, there is after all not many who are going to point a finger at you because you took up your comrades melta gun when he had fallen, and many a mission ends with the acolytes using others resources to reach their goals. But, and here is the big but, they can´t really sell it and gain on it, at least not unless they go to the black market. Think on it, which honest salesman would buy a piece of armour with the Adeptus Mechanicus sigil on it? Which sane person would buy a piece of arbitor armour? And so on and so on. It is like with the real world, if I have gotten my hands on military gear, or from the police or from other originations like that would I not be able to go down into my local gun store and sell it, at least not without the owner of said store taking my name down and then call someone about it.
All of this have only dealt with "loyal" equipment, but what about all the other nice things then? Well what other things are there, there is xeno equipment, that is of course forbidden unless you are really really special. And the last category, equipment made and used by the Ruinous Powers. And do remember that each ganger, each mutant, each and every person who isn´t with the holy god emperor technically falls under this category in one way or another.
I do know that this minimises what a player can do in the universe, but it does also give him a whole new lot of things to work with. Now are there suddenly an extra reason to take a cleric with you, he can cleanse some of the weapons that the mutants and gangers walked with. The tech priest as well does now get a whole new role, he have to soothe the wronged machine spirits, and maybe does both even have to work together at times to purify that armour that the cult leader wore.
This is just my take on loot, and it is properly badly worded and are lacking some nuances and details, because I do know that there exist some "loot" that there are easily sold and brought on the open market, but I can´t properly explain how that fit into the greater system with my limited English skills.
As a little sidenote and extra question, how often do you fellow GMs think upon the rules for requisitioning when you are planning loot and such?