Look, what is your returns policy?
Free Returns - then you are paying return shipping no matter what, so accept the return.
30-day Returns Buyer pays - IF the buyer selects a "remorse" reason for the return, then they pay for return shipping. IF the buyer selects a NAD reason, the seller pays for return shipping.
No Returns - IF the buyer selects a "remorse" reason for the return, then you "can" refuse the return. But savvy buyers know better than select this and if they feel slighted by a rejected return, they will just file with PayPal or their Credit Card so in the long run you lose. However, IF the buyer selects a NAD reason, the seller pays for return shipping regardless of the "no returns" policy. The MBG trumps the "no returns" policy in any NAD case.
But if you use the Ebay Resolution Center return/refund process you have some slim protections. If the buyer is to return the item they have a clock to get an acceptance scan. In some slim cases the buyer doesn't get the scan on time and the seller can ask the case be close in their favor. Also you are not required to refund until the tracking show the item was delivered to you. But there are ways a buyer can scam you so it is best as a newbie to use the eBay process.
But hey, we see sellers all of the time trying to be "nice" and they refund the buyers before they get the item in their hands and then are shocked the buyer doesn't return it. There is no way anyone can "force" a buyer to return something if they are refunded before they return it. So absolute rule - DO NOT refund anything before you have the item in your hands.
Now a caveat to all of that, when returns happen the seller is going to lose money. It is an ugly reality of retail selling. So the amount of money a seller loses depends on the decisions they make and the actions they take or don't take. So in many ways, returns are a exercise in how to minimize losses.
Hope this longer tome lays out the basics. Don't be afraid to ask for clarification on anything,
