In the twelfth book I will include commandments regarding sale and acquisition. And I have called this book the Book of Property. Sale - Mechirah A sale or rental is not final until the proper form of acquisition has been followed.
Real estate is acquired by exchange, by payment, by a bill of sale, or by taking possession.
If the deception is qualitative or amounts to more than a sixth of the price the sale can be annulled. 3,c In all matters of business local customs and civil laws can be followed.