90% of advance notice bookings don't come so I always ask them to confirm in the morning of the booking and i don't hear from them so at least I know they are not coming!
Short notice ones usually do come as they are in the area or been let down by someone and come..
I can completely understand why workers ask for deposits because if you organise an incall for those advance bookings it would be so deflating.
Just the nature of the industry