The can ask the homeowner to show physical proof of title. Not rocket science.

Not unlike car license when pulled over.

My driver's license has my photo and my home address on it.

This would indicate that you reside there, not that you own the location...

I only care about primary residence, any problems that landlords have can be solved by selling all the extra properties they own.

I'm pretty sure the police could just call the town office, at least in my town, and easily verify who owns a home. I would be surprised if the police do not already have direct access to this information.

The problem is that if the criminal is slightly intelligent, they will present a fake lease and/or some mail they received at the address. At that point, it's the court's problem to assess the evidence and figure out if it's a case of squatters or a self-help eviction by a scummy landlord.

Rentals aren’t centrally registered. They just produce a lease signed by someone who says they have control of the house, doesn’t have to be the property owner, doesn’t have to be notarized. So just print something official and say the landlord signed it. The courts eventually figure it out as fraud anyways, but you have six months rent free, and most prosecutors aren’t going after petty fraud, so it’s mostly a risk free crime unless you accidentally occupy a house owned by the mob.