Booking.com Scam Enquiries?

[Casscat]

This has happened to a friend with a holiday rental in my village, although I have not been similarly targeted. We both have small village houses and typically bookings are for 2-7 nights. He had received odd bookings for lengthy stays and is deeply suspicious. This is what he has written:

"Just to make you guys aware I’ve had 2 strange bookings from booking.com within a week of each other, one for 16 nights one person, and one for 9 nights one person, both Russian nationality, no phone number just an address in Bangkok. I found this strange and googled the address which came up with other hosts saying it’s fake and the guests do not turn up (if you Google Prudential Tower Bangkok, other hosts experiences will come up). Although the bookings came via booking.com they were made by a partnering company."

Anyone else with this experience, and how exactly does this scam work, because surely it is a scam? What is odd (well there are several odd things actually!) is that my friend has the option to 'mark credit card as invalid' when surely Booking.com handle all payments? My friend is not involved in taking any direct payment from these or any other guests.