A while back, a European noise musician wanted to crash round my flat on his 'UK tour'. I was like, "yeah, sure, why not?" on email - then woke up at 4am and realised I didn't need a hostile, depressive vegan anarcho-primitivist I'd never met before draped across the sofa. Had to make up some convoluted excuse involving fictional night shifts.
Everyone I've met who's ever let a stranger crash round regretted it. Including a bloke in Camberwell who let Lee Perry doss round his place for a few nights in the early '90s - apparently, Perry was difficult the whole time and smeared his shit over the toilet walls as a leaving present. Another bloke I vaguely knew, a poorly guy from Norway, let an unhinged girl crash round his flat for an 'emergency' 2-night stay that turned into 4 weeks. He came home one day and his CD player and various prescription meds were missing, and the electric meter had been broken into.
More recently, my former brother-in-law took in a mother-and-son duo from Ukraine through the govt sponsorship package, which went tits-up when the kid repeatedly attempted to kill the family cat. Then his mother started screaming when he was firmly asked to leave the pet alone. I also remember a Kiwi woman who went bananas over her Aussie flatmate inviting her pals to sleep on the sofa while they were visiting London, and one of the couch-surfers pouring water into the back of her PC as revenge for being turfed out.
So, just pretend you've got monkeypox and direct them to booking.com would be my advice.