Hire someone with a track record and not "the flavor of the month" or the guy begging to do the work for 1/10 the actual value of the project (and who is always available immediately) and this will greatly reduce, if not eliminate, your problem.
A reputable designer will not overbook themself. A reputable designer is RARELY, if ever, available "RIGHT NOW." A reputable designer will accomodate all your ideas, pay close attention to your notes and never flake on a project.
Seems to me you're not hiring reputable designers
