This seems to be due to asymmetric information between seller and buyer. The buyer can not measure exactly the true area, which only the seller knows (buyer doesn't have access to the standards, the criteria that have been used, doesn't understand them, doesn't have time or is physically not allowed to measure it.)
No. The buyer absolutely can measure the exact area, and can probably do so with a children's plastic ruler, since as near as I can tell nobody rents office space anymore without looking at a PDF of a floorplan first.
Because rsf includes building common spaces, which tenants are in fact renting. This is not complicated.
Yes, it does appear plain that this "common spaces" business is a fig leaf that covers annual rent increases. And yes, that's dishonest. But it's of no practical import, since every tenant knows their rent is going up one way or another once their lease expires.
We're really making a big deal over whether "rent increase" is called "rent increase" or not.