Once you complete an auction and have sent the product to the buyer, it is not necessary that you end your communication at that point.

Instead, you could maintain communication with this future potential buyer by sending an email to them some time after you had sent the product to them. 

End your communication with the buyer by mentioning that they could contact you with any questions in the future through eBay.

And if they do contact you make sure you give prompt answers to them. If the buyer asks for a refund, you have to be ready to give one, if the item is something that may call for a refund. 

Tell the buyer to send the product back to you, and on receiving the item, send the refund to the buyer immediately. All this is quality customer service and positive feedback on eBay site for you!

Once you complete an auction and have sent the product to the buyer, it is not necessary that you end your communication at that point.

Instead, you could maintain communication with this future potential buyer by sending an email to them some time after you had sent the product to them. 

End your communication with the buyer by mentioning that they could contact you with any questions in the future through eBay.

And if they do contact you make sure you give prompt answers to them. If the buyer asks for a refund, you have to be ready to give one, if the item is something that may call for a refund. 

Tell the buyer to send the product back to you, and on receiving the item, send the refund to the buyer immediately. All this is quality customer service and positive feedback on eBay site for you!