when it comes to the hobby for some guys. What these guys are doing to you is totally unfair. They probably are hoping if you will see them on short notice that you won't screen them real hard. Do not shortchange your screening rules just to please a few demanding hobbyists. That is not the norm with most guys, I don't think.
I agree with previous posters, take your phone number off your website and any ads you post, and your profile here, if you have one. Use email, that way you can check them when it's convenient for you. The business you lose will be replaced by more quality clients, IMHO.
From my standpoint, I usually set my dates about a week in advance. I like the anticipation.