... Huh. This actually explains something I'd been confused about before; people on this site claiming that a 1000sqft apartment was small. Which, I suppose, if you include the entire footprint of the apartment including balconies, sure. It would never have occurred to me to do it like that.

For big commercial rental properties they probably don’t care because it doesn’t really push the property value.

I don’t think it really changes the property value because those interior walls are usually cosmetic and not load bearing. If the bank has to foreclose, the next buyer will be well aware they can strip those walls out for nothing relative to the cost of buying the building.

I’m doubtful it pushes the tax revenue for the same reason, everyone is already evaluating based on what it could be.

Smaller units are probably just not worth the effort to manage. It’s a lot of over head to start auditing old duplexes where the owner has a property or two and isn’t a giant company with a whole compliance department.

Why? Banks and cities only care about the price. They also want price to be under and over estimated respectively, neither would want the accurate price, even less so the accurate area.

Could include the size of the pavements fronting the building and the basement with those trash bin also are shared space.

That shouldn’t be the case. In some cases it would also be ridiculous, when the common areas are larger than the apartments themselves (corridors, elevators, technical rooms, etc.). They do include the proportional square footage corresponding to each apartment. But this is still very misleading because some buildings have a lot of common areas that can double the advertised size of the very small apartments.

Holy crap! How do they stop at that speed with those thin bicycle tires?

The parent was talking about it being a "landlords market" and wanting that to be changed. I asked how that might be possible.

Improving advertisements to make them accurate, detailed, and directly-comparable is obviously a good thing. But does not change the market in favour of the tenants; the status-quo exists because of a lack of properties. That means no matter how bad the advert(s) tenants have to choose one available. If there were a surplus of properties then it would be a tenant's market.

(I'm in Europe!)

Advertising is already a pretty strict domain by necessity. We used to allow just about every lie under the sun in advertising, and it was universally bad. We systematically broke that down one by one over many decades, and we're still doing it! I mean, these days you can't even sell tobacco without saying "hey we're trying to kill you btw".

This is a very well-trodden path, I think.

While that would be useful it would not change it from a landlords-market - which is what the comment I replied to was about.

…and define rules for the measurement taken, like no stairs, count areas below roof sloping or outside on balconies etc. with a lower factor, exclude shared areas and cellars/attics, and so on.

Not measuring correctly, not publishing the measurements, or publishing incorrect measurements outside an error margin gets counted as deception. Offer a simple reporting contact point to citizens to report landlords or offers that violate this regulation without a lawsuit.