How do you change that, short of building more?
I hear you guys like suing eachother in the states, seems like this kind of regulation would suit you just fine!
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!)
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.
This is a very well-trodden path, I think.