Be careful if you have to send it out for work. I got ripped off four years ago and lost a CQC-11 and my money that way. A bunch of people also lost Emersons, Striders, Benchmades and CRKs to the same guy. Even guys with positive feedback sometimes turn bad all of a sudden.
If it's extensive custom work with a long turnaround time (over 2-3 weeks), try not to pay the full amount upfront, no matter how they try to persuade you. If the knifemaker/etc won't take a deposit, try and find someone else. Losing $100 is the lesser evil compared to $200+ if it goes south.
That being said, there are established guys who've never let their customers down.