@C121 Be aware that Airbnb only collects the first month upfront. If they're unable to collect any further payment, the booking is no longer an Airbnb booking. But if the guest still refuses to leave, and they've also acquired tenancy rights, you are completely screwed and there's nothing Airbnb can do to support you.
They also don't do deposits or credit checks or any normal things that you need for long-term rentals. All in all, taking bookings of 28 days or more is extremely risky on Airbnb, especially when you have a new listing that's a prime target for scammers and squatters. If you're not prepared to lose huge amounts of time and money to eviction proceedings, don't do it.