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Final note: I just hoped such behavior can be punished if i can provide all the needed information.
The forum will not penalize such behavior, the forum will not interfere in a user's business affairs. Even if you are looking for a defense here, the consequence is simply the tagging of members which is sometimes subjective.
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Here is the whole private conversation with him, even though he already deleted a lot of his messages:
In this conversation, I don't see him billing you upfront for announcement post at a specific payout rate. For the moment I can say that it is not your obligation to pay anything in this case.