Mercar buy, sell, and trade Site allowed someone to lie and say they received an emty package. I did not get paid for my item San Francisco California

I sold a burberry poncho on this site that allows you to sell used or new items. After the buyer received her item she messaged me saying she recieved an empty envelope. (The post offcie won't deliver a empty envelope and I have a receipt with the weight). I informed the buyer that it had weight when I shipped then she messaages me and says "It was filled with tissue". I messaged mercari informing them and they they replied with a standard email that was irrelevant to my concerns. The buyer then filed a complaint and sent pictures to them of the envelope with nothing inside. Mercari canceled the order on her behalf and suggested that I make a claim through USPS. My concern is that they have allowed a buyer to say she recieved an empty package without properly investigating this matter. So I am out of my item and did not get paid for the item that I shipped. They reimbursed her money within 24 hours without looking further into the situation. Just because buyer sent them pictures of an empty package does not mean that she did not receive the item. I strongly believe this buyer scammed because she is aware of how it easy it would be for her to ge away with it! They are basically protecting scam artists!! I have read other reviews online of others saying similar things. 

Signed,

Myka M

email: (((REDCATED)))l@yahoo.com