Earlier quoted context omitted.
Taxing vacant real estate is another tool used in some countries and cities. One way of doing it is via an imputed rental income: if a property is not owner-occupied, then the owners are deemed to be earning a rental income (either market rate, or if rent-controlled, then whatever the set rate is), regardless of whether they actually bother to rent it out or not. That increases the cost of sitting on empty housing. (…
Yeah, something like that might work too, although it can be kind of invasive in the sense that now you need to check if people are living in a place. In Italy, that meant that the police send someone around for a look inside the house where you say you recently moved to. In theory, at least - they don't always.
You can get away with some cheating there, e.g. a couple who live together can claim to be living separately and rent the second one out under the table, or someone who lives with their parents can be dabbling in under-the-table real estate with an investment property they don't really live in. But it at least keeps it to that kind of small-scale thing; the couple can pretend to owner-occupy two properties when they really live in one, but they can't do it with five.