I have learned recently (again), to ALWAYS have some sort of a contract. I took on a railing job for a good bit of money on a handshake. 1/2 down, remainder when it was done, before installation. Well, the lady DIED. Now her estate is in probate, the lawyer is demanding a contract before payment. To make a long story short I have 2 rails completed outside my shop, and no dough in sight. Get some sort of contract with a signature, or it can cost you.
My Dad always said, if it costs you pain, blood, or money you learn from it. Sometimes you get all three.