Lost money on a transaction

To whom do i speak to on this board to warn others about this person.

Sent money. Didnt receive parts. Not responding to emails.
There is an app now that brokers online sales now. send part somewhere, buyer sends money somewhere...when 3rd party gets both they make the final forwarding. You must sell it on that app though. Cant remember name but its advertised online. Iirc they take a cut naturally. Can always ask seller to send you a private ebay listing so you can roll the dice with ebay protections.