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            Under Article 50 of the CISG, if the seller delivers a good that does not conform with the contract, the buyer may reduce the price in the same proportion as the value that the goods actually delivered had at the time of the delivery bears to the value that conforming goods would have had at that time. In this case, the buyer acts unilaterally and is not subject to his/her resort to the court and substantiating the lack of conformation before it, although, in any case, the convention provides remedy for the buyer resorting to an undue option. In some cases, in Imamia Jurisprudence and Iran Law, as where there is the claim for some portion of the object of sale belonging to the other and the buyer may be able based on option in sales unfulfilled in part to get some portion of the price and, in some places due to defect in the object of the sale, may cancel the sale or keep it at the price of getting compensation; they all can be legally considered as instances of price reduction. This paper attempts to compare the instances of price reduction in the 1890 Convention, Imamia Jurisprudence and Iran Law, and while putting the concept of price reduction in the Convention, examines its similarities and differences with the ones in Imamia Jurisprudence and Iran Law. In the end, it is discussed whether this option can be possibly applied as a rule in other transactions or not.      

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   The Contract of Sale as one of the most exchanged contracts requires each parties to perform The Obligations against the other Party. According to the Vienna Convention, the Seller is required to perform the Obligations against the Buyer. The question is that whether Usage is effective in determining of The Obligations of the Seller based on the Convention on the International Sale of Goods? Parties to the contract are not required to predict and specify all details of the contract, It is sufficient to reach an agreement on the elements of the subject matter of the contract and Usage and Supplementary law determine other details and the effects of contract (specifying the rights and obligations of the parties about it). Article 220 and 225 of the Civil Code confirms this claim. Usage also have an important role based on the Vienna Convention 1980, because, in the Convention on the International Sale, in addition to being, the parties are bound by any usage to which they have agreed and by any practices which they have established between themselves, are considered, unless otherwise agreed, to have impliedly made applicable to their contract or its formation a usage of which the parties knew or ought to have known and which in international trade is widely known to, and regularly observed by, parties to contracts of the type involved in the particular trade concerned. In this Research will examine the effect of Usage and Practice in determining the Obligations of the Seller. By induction under the provisions of the Convention, we get the general result  that, in the assumption of the absence of an agreement on the determination of sellers obligations, according to Article 9 of the Convention, Usage and Practice will undoubtedly determine the sellers obligations.Therefore, in the absence of an agreement between the parties on the commitment to certain Usages and the lack of Practice among them regarding the Sellers obligations, if the conditions of the Usages referred to in paragraph 2 of Article 9 of the Convention exist, the seller will be obliged to comply with it. Finally, in the absence of decisive rules, the Seller is bound to fulfill its obligations, In accordance with the Supplementary Provisions of the Convention. The same situation exists in the Iranian law.
 

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Under articles 37 and 48 of the United Nations Convention on Contracts for the International Sale of Goods (CISG), the seller is entitled to cure the lack of conformity of the goods due to specific circumstances. The same legal establishment has been accepted in the Article 7-1-4 0f the Unidroit Principles of International Commercial Contracts (UPICC).
Anticipating the seller’s right to cure, one controversial issue raised is the status of the buyer's right to avoidance. Subsequently, the question arisen is whether the seller's right to cure is prior or the buyer's right to avoidance. While there are various interpretations of Article 48 leading to disagreements, in UPICC, the buyer has no right to avoidance in case of seller’s cure under Article 7-1-4. Similarly, according to general principals including Article 478 of the Civil Code in Iranian legal system, the buyer has no right to terminate if the seller is ready to cure.
To conclude, we can say the seller’s right to cure from the perspective of the doctrine, judicial precedent, legal and economic analysis has priority over buyer’s right to avoidance.