I tend to not deal with artists that have a reputation for taking your money up front and then either never contact you again or spit our endless excusses for not delivering on the promised date: "I got the flu", "my house was lost in a flood", "I broke my wrist", "my dog died"....etc. I cant tell you how many Ive heard these excuses (even the same ones over a period of months - hey at least get some new material! ).
Seriously, I insist on always paying 1/2 up front and the rest upon completion. Paying half gives you an excuse to b_itch about them being late!