拒绝索赔有很多种原因，我们来看看一些常见原因的表达。

1. On going into the matter you mentioned we find that the poor performance of the engine is due to your incorrect use of a different motor oil.
我们对你方提到的事情调查后发现，发动机故障是因为你们误用了不同的机油。

2. Items like this are not to be returned once they are accepted by purchasers. We have established this regulation for offering our customers the definite best quality products.
此类商品一旦售出就不能退换。我们立此规定是为了向顾客提供绝对上等的产品。

3. This is exactly the first complaint from our customers, from which we can understand you have met much inconvenience in satisfying your users.
这确实是我们收到的第一封索赔信，我们可以理解您在满足用户需求方面的许多不便。

4. All the items for export must be under the tight seal which ensures that we always put the Total Quality Control into execution.
所有出口品种都必须真空密封，以保证全面控制质量这一措施的实行。

5. Our investigation reveals that the articles we packed were identical with what were listed on our invoice. We are afraid that the cases you mentioned must have been unpacked during the transit. We are enclosing a copy of the invoice for your reference and suggest you make further inquiries at your end.
我方调查结果表明：我们打包的东西和发票上的一致。恐怕你说的那些箱子在运输过程中被人打开过。随函寄去一份发票复印件，建议你方进一步调查。

6. We are extremely sorry for the late delivery of your last order. It is due to your delayed opening of the relative letter of credit.
非常抱歉上一批货交晚了。因为你们的信用证开得太迟。

7. As stipulated in the contract, a minor discrepancy in colors is permissible. That is why the case you brought up is still under a normal practice.
如合同所示，颜色上的轻微差异是允许的。故此，你提出的情况依然属于正常做法。

（例句来源：《国际商务写作教程》，对外经济贸易大学出版社 英语点津 Annabel 编辑）