Try to call paypal and explain the situation , if they don't believe and they leave the Chargeback as it is then there is two options :

1. Make a new fresh Paypal account. (I would do that)
2. Deposit the required money on the current Paypal account and get your balance back to normal . (I wouldn't do that If I were you).

Also It would be better if you could give us the name of the member on the forums so we can leave him negative trust on his profile and he don't scam more people . [You will have to provide proofs though]