This is based on a concept called price parity, for which there are exceptions - including opaque rates, packaged bookings, and last minute / mobile. HotelToni

This is based on a concept called price parity, for which there are exceptions - including opaque rates, packaged bookings, and last minute / mobile. HotelTonight is able to fit inside those limitations when selling rooms last minute - so they are indeed often cheaper than other aggregators or booking direct.