…which makes you a business. You’re making income from rentals. A landlord who has 500 units but can’t seem to fill them but once or twice per year for a weekend doesn’t suddenly stop being a landlord. And if they told me “I’m just supplementing my income” in order to get around installing fire alarms, I’d laugh in their face.
If you’re providing a commercial service to strangers, you should be able to ensure their safety, full stop. If you can’t afford to do that, you can’t afford to provide the commercial service.