This is currently an inefficient market, and more information would substantially improve it. And objectively measuring square feet is not particularly difficult or expensive.
What will probably happen is, eventually the misrepresentation of square footage will get so egregious that there will be a movement by commercial renters toward some sort of third-party measurement. The landlords will go along, because they want to rent their office space.
The first complication with this suggestion is that in cases of exploitation of information asymmetries like this, you don't know what you don't know. It's nice that this issue is getting a little public scrutiny here now, but one has to wonder how long it's been going on? And getting an issue like this more widely recognized, to a point where demand for transparency would be self-sustaining, is likely to require a lot of someone's time an effort to bootstrap. If a subset of buyer/leasers were to take this on openly, real estate owners would almost certainly seek to punish them directly, in addition to mounting their own counter-education campaign >>> politicization. Alternately, some third party might sense a commercial opportunity here, e.g., to provide public education and neutral measurement services -- but that's the same sort of business model that makes "trial lawyers" so popular...
It's unrealistic to assume that commercial renters are going to be broadly responsive to individual demands for transparency before the overwhelming majority of real estate seekers permanently embrace transparency as a make-or-break requirement for buy/lease decisions.