I used to sell on Mercari with a 5 star rating, until they gave my product away. I sold a piece of sports memorabilia that the buyer reported damaged (8x10 protective plexi-glass sheet reportedly cracked). The buyer removed the triple layered protective foam sheets (which was more expensive than the $1 plexiglass sheet), took photos without the protective measures and sent it to Mercari. Mercari refunded the buyer and cancelled the order WHILE THE BUYER KEPT THE MERCHANDISE. They responded with, "merchandise was insufficiently packaged" and hazardous to return.
I have shipped close to 100 (93 to be exact) of the same type items (all exact same materials/sizes/packaging with zero issues.
So, if you would like to receive items for FREE, remove any protective measures, file a damage claim stating broken glass along with doctored up the photos, and they will take the buyers word and give a 100% refund and let you keep it!
Sad, but true.