How do you prove a building is empty? "Do you have a lease contract?" Easy to get a lot of $1 contracts... "Did you use water / electricity?" Easy to leave a

How do you prove a building is empty? "Do you have a lease contract?" Easy to get a lot of $1 contracts... "Did you use water / electricity?" Easy to leave a faucet running or set up bitcoin miners. If you go on word of mouth? What about false positives -- I travel for work and keep an apartment in one city and my house in another. Would that be a problem? I don't know how to penalize empty apartments in a way that isn't really easy to game, or unjustly fair for people who don't just live in one place.