In my experience the vast majority of businesses will not entertain the idea of cash up front, period. I bet that you wouldn't either. If you were building a house, and the builder demanded cash up front, you'd laugh in his face.
Finding good clients is important, but if you demand to be paid in advance, get used to waiting those tables because you're going to be doing it a long time. Note: you will not be paid in advance for waiting those tables, either.