or you can test their wits. Welcome them as if you are expecting them, shake their hand, then invite them into your home and have a table set up with a full on dinner. If you got family, sit them around the table. Tell the customer "have a seat." When they mention the item you are selling, act confused. See how they handle the situation when they realize they are in a strangers home, possibly the wrong house, and you have them confused too. I do it all the time.

If you really want to throw them in a loop, send them back on the road, then when they call again, give them the same address and describe the house they were just at. Then, when they come back, you can kill them and burry them in your backyard.