Sale of flates and sales return by builder

A builder has sold few flats and shown the same as sale. Now, buyer is not paying sales consideration, therefore, builder wants to shows the same as sales return. A period of about six month has passed after the sale. Hence, prices of flates have increased.

My question is at what price sales return should be shown ? (i.e. at the same price at which it was sold or at the price prevailling at the time of sales return) Kindly support the answer with relevant accounting standard.