I have less problem with asking for everything up front, especially in cases where the art will be completed in c. 30 days. If something goes wrong on the artist side, they can get their money back via paypal. (For larger projects it can work step-wise, where you still pay for the 30 days worth of work.)

Either way though, it's the commissioner's project. Why should the artist invest before the commissioner invests a dime? At least that's the way I look at it. It also saves some trouble with "But I wasn't 100% sure/ready/something came up"