How do I post correctly about this issuse that everybody else sees it. that this user is a scammer?
This is correct. Follow the dispute resolution process.Open a thread in "Dispute resolution" and provide all of your evidence:
https://www.blackhatworld.com/forums/dispute-resolution.31/
Example:
Dispute: @Prehisto v. @username
How do I post correctly about this issuse that everybody else sees it. that this user is a scammer?