If I was renting out an AirBnb in Germany I'd probably just set up a travel router that pipes everything through a VPN in a neighbouring country.

Someone I know who owns a hotel in germany said it happens so rarely that it's cheaper to pay the fines than maintain router configurations or spend time to dismiss them.

The hosts should have a kind of protection in case downloading illegal stuff is happening in their stays.

Wouldn't that be more a legal thing? A bit like you can't take out insurance against speeding tickets. I guess they could offer some sort of insurance for covering your legal fees to deal with such things, though.

Yeah, sounds like a law the state/country would need to make.

Add the cost of a router that supports e.g. Mullvad and the monthly subscription to the rental cost, then advertise "uncensored Internet" as a feature.

Can’t you block a router to block all torrents?

You could try blocking ports used by P2P frequently.