1) Update your product descriptions to accurately reflect the watches and watch sizes that it fits. I have a 41mm and it does not fit - see video I shared.
2) If your product does not work as advertised, and your support suggestions don't fix the issue, offer to give a full refund and to cover return shipping.
3) Never expect the customer to pay for return shipping and a 5% transaction fee when your product is faulty.
4) Don't repeatedly tell your customer that they are returning for 'persona