1) As a seller, you are responsible to deliver paid for goods as any seller is. You are responsible until it reaches the buyer.
Putting it in the mail does not absolve you of this responsibility. If you fail to insure the knife and it becomes lost, you are responsible to refund the buyer and take the loss for your negligence in not protecting yourself or the buyer.
2) As a buyer, you are responsible to report problems immediately to the seller and try to work out a solution in an amicable manner. This does not include any modification, tinkering, cleaning or maintenance of your item. Once you've tinkered with the item, it is yours.
Putting it in the mail does not absolve you of this responsibility. If you fail to insure the knife and it becomes lost, you are responsible to refund the buyer and take the loss for your negligence in not protecting yourself or the buyer.
2) As a buyer, you are responsible to report problems immediately to the seller and try to work out a solution in an amicable manner. This does not include any modification, tinkering, cleaning or maintenance of your item. Once you've tinkered with the item, it is yours.