I was a dj in a bar and I received tips here and there.  If someone wanted their request played sooner than the ones before them or if they just really liked the music I was playing they would offer to buy a drink or put some money on the table in my booth.  I never asked and alot of time would try and give it back, after all it was my job to play music.  I guess tips were just a way of them saying, "You Rock!"