Here's how I work ... I think this helps....
I do a sketch BEFORE ANY PAYMENT is taken. Based on the clients needs.
Then ... if they're happy with the direction, I take a 50% payment. This ensures the job for both client and artist. Then, we detail the sketch, and then we move to final ... and when final is done, I deliver and take the last 50%

So I start work before any money changes hands.