I recently finished my 11th knife, and was almost forced to take the full price of it, as it was for a classmate's Christmas present, and she wanted to make sure she did not spend it. In the end I took the money, making sure that she knew it was going to be put away until delivery of the knife, and that she would have the choice of the knife or the actual money she gave me. That was the only way I was comfortable with accepting the money, especially as I am such an inexperienced maker that I never feel that it is good enough (good thing the end users seem to disagree!).
I have been on the purchasing end of a couple of long term projects. A couple went well over expected time frames without much contact but I got the knives. I was given both the best experience and screwed royally in the WSS FB knife a couple of years ago, which really opened my eyes to the situations. NWA was fantastic, updating the group on status and time frame, and as such everything was great. Ironwolf, the other maker, hid, threw the knives together quickly, and ended up not sending me 2 blanks that I paid in full for, and has stopped responding to me (I still write from multiple accounts every few months asking him to man up and make things right after stealing my money). I may work with small deposits in the future, but it will be rare and the person accepting the deposit must have an account set up to not use the deposit until my knife is ready (more as confirmation of my seriousness, so it will not be much). Just my rambling on the topic.