I think I am with Christopher. These are non-essential items - contract for one any way that makes you comfortable. If you are comfortable with non-refundable deposits and no guarantee date, then why not? Enjoy your life.
If you are like me, just stand back, watch, and applaud the state of the art. I love Daylight Northerns, and really enjoy the Marsh pictures. But I'd rather build my own.
If you contract with Kohs or MMW for a large deposit, get your conditions in writing, and get it signed. Easy.