Personally, I've never had payment issues with long-term guests. I have occasionally received messages that there was a problem collecting the monthly payment, and this message comes speedily, but that was always resolved by the guest (who also gets messaged I assume) before I even had a chance to ask about it. The only real issues I ever had turned out not to be non-payment from the guest, but Airbnb glitches (i.e. Airbnb had the money but was withholding the payout for no reason).
Of course, that doesn't mean this this 'loophole' can't be used by scammers, but I am not sure going off platform with no other protections is a great idea wither. You could easily end up with a squatter and o chance of help from Airbnb.
I think that if you're going to host, you need to vet all guests, and especially the long-term ones. I insist on verified Govt ID, profile photo, agreement to house rules and some info about the guest at the minimum. A lot of hosts seem to be willing to take any booking that comes along. My rules also say the guest will need to show their ID on arrival. I don't actually ask them to, but it's there as a deterrent. People will say my rules are far too long, but they can certainly also be a very effective deterrent to those planning to mess a host around.
Above all, it's important to know the tenancy laws in your location. If this guest stops paying and won't leave, do you have the right to kick them out and how? Is it straightforward, or do you have to go through the courts? I've only ever asked one (long-term) guest to leave and that was straightforward. Actually, I asked Airbnb to ask her. In my experience, guests take Airbnb far more seriously than an individual host.