I chose the hotel based entirely on its nice location in the center and next to the railway station. After traveling 12 hours I arrived in the hotel 10pm on Saturday night, and heard that they were "fully booked". After explaining that I had one of those bookings, I heard that hotel booking system allows overbooking through third party hotel booking services, and my booking was one of those "excess ones", and was offered a room in their "airport hotel", where I would have a free taxi ride. With no interest nor energy to start hunting new hotel, I accepted the offer puzzled by questions "if they knew there is overbooking, why nobody informed me" and "how can they still charge me the same fee".
New hotel was school-alike building in a residential area, 5 km away from center, so I gave up the plan to get familiar with Frankfurt nightlife, and went to bed to get at least good sleep. But of course in the morning, before the wake up call, the first airplane woke me up.
Although people were nice, the treatment was bad. Never again.