I had an awful holiday experience through them and they pretty much blamed it all on me. I booked an apartment and requested 2 travel cots as part of the booking for the 2 new born babies that were travelling with us, no travel cots there and booking.com said it was my fault for not getting in touch with the venue directly to make sure we had them.
We were stung with a €150 bill as soon as we get to the venue for a city tax that we knew nothing about. Booking.com admitted that they usually add this to their confirmations but a computer error occurred and didn't print with our confirmation but again it was our fault apparently for not doing our own research to see whether that particular city had a city tax that we would be liable for. Their customer service was awful and I just don't understand what their use is if they're not responsible for giving us the vital information that we need for our holidays. This is the first and last time I will ever use them