I ask my clients for a 50% nonrefundable deposit on anything exceeding $250.00, however few of my jobs go over a couple of grand. It mostly covers materials purchase and pick up. It's really up to your contractor because we/they aren't going to get shafted on signed contracts with an order to start then tie up our own money in materials for a job the client may back out of. Like home builders everything is written in their favor. They will determine what they want.
"We're going to take things away from you on behalf of the common good"
Sen. Hillary Clinton - Speech at Democratic Fundraiser, June 2004