@Linda324 I was opposed to the oath from the beginning, and I still won't sign it - and what you're pointing out here is another reason for that: it is not a reciprocal agreement. All a guest has to do to get their stay refunded out of your pocket is complain that you didn't follow the arcane rules to the letter, but there's no oath of obedience for guests. This is overall a bad contract.
That said, I think the question of whether a guest "knowingly" has COVID is a red herring. As many as 40% of recorded infections are currently thought to have been passed on by an asymptomatic carrier, and this at least illustrates how useless self-reporting is here. I'm not entirely sure what you mean by "host's liabilities" (specifically, liable to whom?) but since your listings appear to be fully self-contained and detached, it appears plausible that they could be used as quarantine locations. And anyway, if you signed onto the cleaning protocol, you're committed to cleaning the property as if it had hosted a Corona-positive guest anyway - so I don't see how it would make much difference if they happened to be aware of it at the time.
Whether you're liable for enforcing quarantine orders (for example, preventing the infected guest from leaving the property) comes down to your local laws.