The way I would look at the deposit scenario is this, does the person developing the model have a past history of delivering good models. If the answer is yes and I want the model then I put down the deposit. If the answer is no then I walk away - there was a proposal for a Leader locomotive a couple of years back, there was no history behind the person doing the model so no way I was going to put money up front.
Now if it is a retailer doing this, I am not so sure I would want to put in a deposit as there are now multiple parties involved and more of a risk of one of them going down and my money with it. If it was Hornby, Dapol, Bachmann doing it, no I wouldn't, they are big enough to stand on their own two feet. Then there is DJM, new company, old name - difficult one and I am glad that Dave has gone down the route of putting his money where his mouth is because although I believe he is honest and will deliver good models he has no current history in doing so on his own.