Doing the work before getting a commitment is designing on "spec" and professional designers don't work that way. The AIGA guidelines point this up. For me there's a 1/3 deposit of the agreed upon price due before any work begins; another 1/3 is due upon acceptance of the design; the balance upon completion of the job. This keeps us ahead of the game, as we're always received the money to cover ourselves before we do too much work. The final payment is the only one that would put us behind in the profit area (but never at a loss) and if a client balked at paying they wouldn't get their finished job and would have already spent 2/3 of the total non-refundable cost.