Thanks for sharing. I save it in my lists.
I used to work in IT on big project in France, and my company was asking a prepayment of a third of the agreed price.
A first payment before starting is a proof that the client is ok, has fully understand the conditions, and takes thing seriously. In case things goes wrong for any reasons, it ease a lot conciliation in your favor.
If the client can't pay, at least you didn't lose everything. Also if you can check the solvability of the client with a notation agency report it is one more security.