Article 35 CISG
(1) The seller must deliver goods which are of the quantity, quality and description required by the contract and which are contained or packaged in the manner required by the contract.

(2) Except where the parties have agreed otherwise, the goods do not conform with the contract unless they:
(a) are fit for the purposes for which goods of the same description would ordinarily be used;
(b) are fit for any particular purpose expressly or impliedly made known to the seller at the time of the conclusion of the contract, except where the circumstances show that the buyer did not rely, or that it was unreasonable for him to rely, on the seller's skill and judgement;
(c) possess the qualities of goods which the seller has held out to the buyer as a sample or model;
(d) are contained or packaged in the manner usual for such goods or, where there is no such manner, in a manner adequate to preserve and protect the goods.

(3) The seller is not liable under subparagraphs (a) to (d) of the preceding paragraph for any lack of conformity of the goods if at the time of the conclusion of the contract the buyer knew or could not have been unaware of such lack of conformity.