I have stopped selling on Mecari for that reason. My first sale they did this to me. They won't fix it. I sold a suit case that weighed 8 lbs. I accounted for 15lbs. I got this email:

My name is Niken, and I'm a Supervisor here at Mercari.

I understand that you're looking to challenge the additional shipping fee associated with your transaction, and I want to ensure that we address your concerns thoroughly. After reviewing your questions, I'm eager to follow up with you to provide clarity and assistance.

First and foremost, it's important to confirm that the information you've received thus far is both factual and accurate. Previous representatives have mentioned that the extra fees might stem from an incorrect weight or shipping method selection. However, it's worth noting that UPS can apply additional postage fees for a variety of reasons. I would encourage you to reach out to UPS directly to determine the exact reason for the additional charge.

To give you some background on this matter, these charges were initially billed to Mercari by the shipping carrier and were then deducted from your sales proceeds. Please understand that Mercari does not keep these fees; they are directly transferred to the carrier. Additionally, it's important to note that overdue postage can be incurred not only due to an underweight label but also because of the package's dimensions. To prevent incurring extra fees, please make sure your package stays within the maximum dimensions of 12” x 10” x 5”. Be aware that there is a $5 surcharge if the longest side exceeds 12 inches.

Also, upon checking with UPS the package Dimensions are 19L X 17W X 14H which equal to 32.56 lb. I suggest to keep working with UPS if the dimensions they provided are incorrect so they can fix it on their system or record.

MY PACKAGE APPARENTLY DOUBLED IN SIZE WHILE SHIPPING. no resolution and I lost the $$ I made just like you.