This is true, but I remember reading an article where the journalist compared the "only X rooms left with these conditions" claim to the system of the given hotel in real time. Well, as it turned out, the hotel had more than X free rooms with those conditions allocated to booking.com...

Booking doesn't care, though. They'll happily overbook the rooms you assign them sometimes.

Edit: It might have gotten better since, but I still remember all those sad/defeated/angry faces of people who had booked trough Booking.com that I had to send away / find alternative hotels for because we were full. Back then when.

I had that in Asia quite a lot with Booking; that's not my problem though; it's theirs. But that's why I do not use them (booking) whenever I can prevent it. Hotels.com has this rarely but when they have it, they make sure you are well taken care off; I got much better and far more expensive hotels for the same price in those cases. I discovered ny favorite hotel in the world (so far) by a double (double double; the overbooked twice for the same room) booking; everything was full so they booked me in a hotel in the middle of a nature reserve which was much more expensive at that point, but I paid nothing more of course. Very nice for a business trip where I was supposed to sleep in a concrete bunker in a city.