@Everton25 Well, I'd be curious to know how your host friend determines that there are irregularities. Airbnb doesn't release information to hosts about payment methods of guests.
One thing I can tell you is that same-day or reservations made within 24 hours of check-in are the most suseptible to having non-payment issues. Because the guest can check in before Airbnb gets a notice that there are insufficient funds, or that the credit card isn't valid. For myself, I have a 3 day advance booking setting. I want to make sure that the payment goes through before the guest shows up.
I know this advance booking setting wouldn't work for hosts whose main business is made up of lots of same-day or last-minute bookings, though.