CAROUHELL EP3: lost mail is it the seller’s fault?

OHHHH NOOOOO :(((

This is the first time this actually happened (am a great believer of singpost haha because what else is there to use right?)

So I was selling this brand new baggu bag at less than cost price ($73 on official from US) and I rejected buyer’s offer of $60 which after she agreed to buy at $70. Subsequently she asked for free mailing and I asked if normal mail was ok. She asked other questions then agreed and paid $70 to me. Mailed out the item via normal mailing which I didn’t put a return address (I mean I thought only tracked mails need return address!!!!).

SO UNFORTUNATELY ITEM WAS MISSING!!! (Actually I mailed 2 other items tgt which were all delivered successfully).

Buyer asked to refund half the item but I rejected because ? you agreed to normal mailing which won’t be fair to me if I have to be liable too right? She insisted that she did not agree to normal mailing and have no idea how it works. She also said that I listed free tracked mailing on carousell (it was $1.99 tracked mail by carousell which she didn’t buy through). Contacted singpost and they said they can try to find it but really no promises 😭 then here comes the 1 star review

SIGH is this the seller’s fault? I mean she really might have missed out the message and really dk what normal mailing is BUTTTTTT you don’t have to be mean and review and imply that I got no common sense right…. I have buyers agreeing to normal mail for even pricier items or they will just top up for tracked mail or if they are really worried they will buy through carousell.

What do you all think? Seller or buyer’s fault?