I think the appointment book is the best way to go about it, you have to protect yourself, and your furbabies.
As a buyer, i would understand that breeders are very busy, and as long as i got the see the new puppies, the dam, the living conditions, and a few of the other yorkies living there (with out handling the dogs, only the puppies if they had there shots). I dont think making an appointment is a bad idea. I would always have a friend or my husband there to help keep an eye on all of the furbabies (counting heads, if you will
) You need to feel comforable, and your buyers need to feel comforable too, but need to be respectful coming in to your home.