I don't know that Admins would take the time to authenticate the PM's. I would say OP showed their work on this just fine using the screenshot of the PM's they were able to receive in an attempt to prove availability of accounts for sale. That being said zackie has been shown a way to prove their claims that they were hacked didn't notice and then came back to see the tag. What more proof would you be looking for apart from the image showing received PM's? There are also chat logs to back them up.