[For more current case annotated texts by this author, see Bernstein & Lookofsky, Understanding the CISG in Europe, 2d ed. (2003) and Lookofsky, Understanding the CISG in the USA, 2d ed. (2004).]
E. Buyer's Obligation to Return Goods in Condition Received
313. It follows from the general restitution rule that a seller who has delivered the goods either wholly or in part may claim restitution from the buyer of the goods supplied. Article 82(1) sets forth a corollary of the general rule: the buyer loses the [page 168] right to declare the contract avoided if it is impossible for him to make restitution of the goods substantially in the condition in which he received them. At the same time, this principle applies in cases where the buyer demands that the seller perform in natura by re-delivering substitute goods: the buyer loses the right to demand redelivery if he cannot return the goods in the condition received.
F. Exceptions to the Return-of-Goods Rule
314. The general rule (that the buyer loses the right to avoid and to demand redelivery if he cannot return the goods in the condition received) is subject to three exceptions.
315. First, the buyer need not return goods substantially in the condition received if the impossibility of making such restitution is not due to the buyer's act or omission. Under this exception, the buyer is relieved of his duty to make restitution not only where the deterioration of the goods is attributable to the seller, but also where the goods are lost or damaged due to force majeure or the act of a third party. It has been suggested, however, that this limitation relieves the buyer of his duty to make restitution only in cases where he has exercised reasonable care in protecting the goods.
316. Secondly, according to Article 82(2)(b), the buyer need not return goods in the condition received if the goods (or - as is more likely - part of the goods) have perished or deteriorated as a result of the examination provided for in Article 38.
317. Finally, the buyer need not return the goods in the condition received if the goods or part of the goods have been sold in the normal course of business or have been consumed or transformed by the buyer in the course of normal use before he discovered or ought to have discovered the lack of conformity. In this case, however, the buyer must account to the seller for all benefits derived by such sale or consumption.