Both happened to me. I booked a place in New Zealand, and a few hours later, I was contacted that the reservation was cancelled. I later saw the property relisted.
I also booked a place in Seattle that a few days later it became obvious that it was a fake booking. For a couple months booking said it was legit. Finally, I decided I was done with booking and made other arrangements. While in Seattle, I walked over to the condo building that was shown in the booking photo and asked if any of the units was being rented through booking. I was told there were four units, none of them being used for short term rental.
I use them for scoping out possibilities and I'm trying to avoid using them.