Suspicious Return Requests Of Buyers Accepted By Mercari

In the past week, I've had two folks try to return stuff. One claimed the box that was left on their patio wasn’t there, which was declined by the carrrier.. assured them I had evidence and involved their post office supervisor, who confirmed delivery. After I told tham all this, that changed their mind and said one of their neighbors took the package in so it won’t get lost, really? another said the plastic item I sent shattered, despite others being fine in the past. What they ordered was only $5, they should’ve discussed with Mercari throughly but they just made me refund…so unfair and def not how sellers want to handle things when there is a suspicious activity.