This letter relates to your business arrangements with the client.
It acts as an acknowledgement of fault on your part.
Accordingly, it must only be used on occasions where you are prepared to accept responsibility, not when you're intending to dispute the case.
It should also contain an offer of an alternative solution to the issues raised by the defective goods. If a contract is involved, cite the contract according to circumstances.
Re: Defective goods / materials
I refer to your letter / email of (date) concerning defective / damaged / unsalable goods delivered to you.
Please accept our sincere apologies for this occurrence, and our assurances that no charge will be incurred by you for the goods or handling costs.
Note: It is intended to arrange for the pick up and return of the defective goods to us by our courier from your premises. Please advise a suitable time and arrangements for this procedure.
As per the provisions of (cite contract clause) of our contract, we will refill the order, and ship it to you immediately by special delivery.
Please advise your acceptance of these replacement goods upon receipt by letter or email.