Not to mention it's that last 20% that takes the longest time/effort.
i.e. someone can do a quik vacuum and be done with it fairly quik, but if you really go all out and get every nook and cranny, meaning under the seats where it's never been done and in between the seat cushions, seats, everywhere and a proper job can take an hour if the vehicle is halfway trashed when you start on it.
I did a customers PT Cruiser for the 1st time today and it looked like it hadn't been vacuumed in well over a year.. It took me nearly an hour to finish the interior and it wasn't even a "detail" [meaning I didn't scrub any carpets or seats] But I vacuumed that thing as good as possible. When I was done I made sure she came out and walked her through, opening every door so she could see there wasn't a grain of sand or dust to be found inside.
She said the magic words "wow it looks like brand new" and I got paid
I'm still working on ways to get faster... But I'm not so sure that same job gets done in a quikie.