Well, Im just the opposite - I pull the liner/carpet out, pull the spare out, vacuum everything really good, look at the tire and wheel and if its trashed, lightly get it back to normal, check the air pressure in the tire, adjust if needed, and put it all back...
I Never - take the Battery out unless its requested, as this may cause all their things in memory to be lost, and the computer will have to reset it self and re learn its former settings..
All Bimmers have the battery in the passenger side rear fenderwell in the trunk so I am so familiar with this part.. All Bimmers have a Battery vent tube that gets the gasses out and I have never see one in hundreds that had an issue in that compartment, they are always clean, dry, and happy looking..
I never take the jack and tools out unless they are already out and then I just put them back the way they are supposed to be..
This is also a great time to look for leaks and/or rust in the trunk compartment/floor, so you can tell the Client if they have an issue that needs their attention...
Since I have such a nice Extractor, I will spray the entire trunk carpet lightly with Meguiars APC+, not necessarily brush unless it has some spots, (carpets in most but not all trunks are not very good quality and will be "grabby" with any type of brush, so you have to be careful here), and go over it quickly, 1 - pass -, and it all looks so much better to have all the dirt out of it, and let it dry..
Besides, trunks need to smell Clean too, right ?
All around the trunk Jambs, and the underside of the trunk lid are perfect, not perfectly Polished, unless its asked for and charged extra for..
Steam from my VX5000 really helps get these areas clean fast, and I get all the embedded gunk out from around the back of the tail lights, etc...
If its Detailing, are not we taking care of the Details here too ?
Besides, it all has to Match, right ? Super clean paintwork, interior, dirty engine and compartment, dirty trunk = no match...
Couple of times, I have been caught with a trunk carpet that had some spilled laundry soap in it, so that had to be rinsed quick with a pressure washer (because you will never vacuum or extract all that concentrate out quickly), and then, extract as much dirt out of the rest of it quickly, let it all dry outside, and then put it back..
Always try to use just enough water to do the job, and not just flood everything because this causes you more work...
This should NOT take 2 hours - what are you doing correcting the paint 3x or something ?

Dan F