Here's how I do it, it might not be perfect but works for me.
I first usually get people calling me or by email, either way I ask the normal questions, and then I send them my contract, if they are serious I setup a phone appt, and we have a chat about breed specifics and puppy needs, I ask for references Vet and Groomer, if first time puppy owners I talk to friends and relatives. if everything goes well then I setup a visit, I only receive people friday, saturda and sunday, When one of my men is home. NEVER, Never while I am home alone, even tho I have Niko the Malamute to defend me..
at the home visit we go thru the contract and they are required to leave a $200.00 deposit, deposit can be cash, check or money order.. for the baby. Balance is due when baby is 12 weeks in CASH. They have to come and pick up the baby in my home by appointmen only.
also they have to register the microchip with me as the second contact
and provide proof.
that is what I do to protect me,my puppy and the buyer.