What is the reason for the return, this is mportant.
If it's faulty then you open a case for item not as described, the seller Has to accept this.
If they don't, and don't send a pre paid label within 3 days, you escalate the case to eBay on day 4 and they step in and force the refund. With no label provided in this case, you will not have to send the item back.