Dear :

I've received your letter requesting credit for the [products] we made for you.

Although I can understand the situation explained in your letter, I'm afraid we cannot accept the return of these [products] for credit. They were specially designed according to your requirements and there is no market for them among our other customers.

However, we will keep you informed. If we do get an inquiry for these special products we will let you know immediately.

Sincerely yours,

[name]

[title]