a point view about the compensation of belonging the object of sail to others

because of sailing the estates by non-formal deeds; sometimes the estates of others are sailed without knowledge of the owner. so the dealing will be null by reject of the owner and the seller must amend the buyer’s damages. the main questions in this study are: what is the area of damages? what are the foundations of seller’s responsibility against the buyer? we will study the causality, exchange liability, and the theory of apparent as the foundations of seller’s responsibility. then we will consider if the criterion of appointing the damages arising from differences between the prices and the real worth of the estate at the time of giving the price back, would be a subjective criterion (the worth of the estate being object of sail) or an objective one(the worth of the similar estates).