Its about sold item

Last two weeks, I sold a watch. It is quite pricey as in my country it get to one thousand ringgit for it. My Garmn watch.

The buyer was quite fussy, message everyday. but he paid fast so I proceed with it. He didnt even look at the item on his own. Only by whatsapp video and picture.

I advertised it in facebook. So guess the buyer was from there.I have to post it to him. He is across states.

So today. The buyer ask for refund, said the battery didnt last long. Fyi the watch have warranty up till next year. They didnt hv warranty for battery.

What should i do?