I've bought a fair share of customs, and made a fair share.
Some makers ask for deposits, some don't. There is certainly no hard and fast rule. I recently bought a knife from Little Hen for example, who posted above, who I speak with almost daily on Paltalk, and had no problem sending him half down for my order. It keeps a cash flow for a guy with a family to feed. The knife was delivered in a timely fashion and there was the guarantee I could return it if dissatisfied. Seemed like a fine way to do buiness to me.
As for being wary, I understand. However, almost all makers are very scrupulous, especially since the rep would travel far and fast with today's instant communication. The only caveat I would strike in a deposit deal would be, if the delivery time is inordinately delayed, deposit will be refunded.
In twenty-some years around custom knives, there have really been very few crooks I've ever heard about.....