I don't know if a " half down, half at completion" contract is always required. I have always been leery of people who want money before anything is done, (including lawyers, LOL!) However, I see nothing wrong with progress payments with smaller "up front money". Anybody who needs a large sum at the onset might have some cash flow problems or is under capitalized for the business he is in. One danger is if the contractor is paid in full, but fails to pay his vendors or workers, you could end up with a mechanic's lien on your property. This is the kind of contract that your lawyer (pay in advance) should be involved in.
A better way might be to set up an escrow account with a bank where you have deposited the funds earmarked for the job, and only pay out as the work progresses on schedule. That way the contractor knows the funds are there and the bigger part of the carrot is still dangling.
