At the beginning, when Sam is talking to Diane about the their relationship, Cliff's sleeve is visible outside the door every time the door opens although he hasn't entered the set yet.
As Sam is waiting for the Lodge members to arrive, you can see a bald man looking through the Cheers entrance door. A minute later the same man enters the bar with his wife.
Diane makes an uncharacteristic grammatical error with "... I haven't seen any more customers than there were before you took over as host. In fact, there are less." She should have said, "... there are fewer."