Just thought I'd add a recent data point - I recently made a booking with Olotels for the Frankfurt Intercontinental (w/breakfast). Emailed the hotel shortly after to confirm. Hotel said no reservation so I emailed Olotels. They said they normally don't send the hotel reservations until 2-3 days prior, but they would contact the hotel immediately to confirm. A couple of days later, Olotels emailed me to say the room was confirmed. I emailed the hotel again and they confirmed fully paid room with breakfast. All in all, good, responsive service from Olotels (and a great deal).