Recently a lot of members are being scammed for double spending. The scam is super simple & easy to do so make sure to read this thread and avoid being scammed in the future.
When someone sends BTC to your wallet, you'll need to wait for confirmations. Double spending is when a wallet is sending money to another wallet, and then the other wallet is sending the unconfirmed money to a different wallet. (I think this is the easiest way to explain this )
Which means: EVERY TRANSACTION THAT DIDN'T REACH 1 CONFIRMATION CAN BE REVERSIBLE (LIKE A CHARGEBACK).
Conclusion: ALWAYS WAIT FOR AT LEAST 1 CONFIRMATION
Honestly, all of this happened just because @VenomSlave2 leaked the method.