在国际贸易中，买卖双方经常需要通过信函进行沟通和谈判。当买方发出报价后，卖方可能会根据市场行情、产品成本等因素进行还盘。以下是一篇关于卖方还盘的信函范文（英文）：
Dear [Buyer’s Name],
Thank you for your recent offer dated [Date] regarding the purchase of [Product]. After careful consideration and review of our current costs and market conditions, we regret to inform you that we are unable to accept your offer as is.
As a valued customer, we would like to work with you to reach a mutually beneficial agreement. Therefore, I am pleased to offer the following counter-proposal:
Price: We propose to supply [Quantity] units of [Product] at a unit price of [New Price], which represents a [Percentage]% increase from your original offer. This adjusted price better reflects the recent fluctuations in raw material costs and production expenses.
Payment Terms: In order to facilitate a smooth transaction, we suggest changing the payment terms to [Proposed Terms], which will provide us with some assurance during this economic period.
Delivery Date: While we understand the importance of timely delivery, due to the increased demand for our product, we request an extension of [Number] days for the delivery schedule, ensuring that we can maintain the high quality of our products.
We believe that these adjustments are reasonable and aim to ensure long-term cooperation between our companies. We hope you will consider our counter-offer seriously and look forward to discussing further details with you.
Please feel free to contact me directly if you have any questions or need clarification on any point. We appreciate your understanding and look forward to your positive response.
Best regards,
[Your Name] [Your Position] [Your Company] [Contact Information]
此信函表达了对买方原始报价的尊重，并提出了合理的还盘条件，以期达成双方都能接受的协议。