A bill acceptor 24.2 for a gaming machine includes a receiving zone for receiving a tendered bill. A sensing device 48 is arranged at an input region of the receiving zone for sensing at least one characteristic of the bill A controller 52 is in communication with the sensing device 48 for receiving an output signal from the sensing device 48. An annunciator 58 is controlled by the controller 52 to be activated when a bill acceptance rate of the controller 52 drops below a predetermined threshold.