First time happened few months ago with a guy private messaging me in discord (or telegram) saying that he needed help withdrawing his 1+ BTC and would give some btc as reward as reward for helping, he would get you to make a wallet on the site and transfer, once he transfers you this fake btc he will ask you to withdraw, when you try to withdraw the site will give the following message and asks you to deposit, the scammer here is relying on you to be greedy. im guessing once a victim does deposit it will ask you to deposit further times and then the dude will probably block you after he got his monies.
2nd time i got contacted by someone "from china" and asks you to help him cash back btc because of China crypto ban, you can see one user here on another thread exposing the scam site with some technical information, props to him; https://bitcointalk.org/index.php?topic=5070938 once the scammer does this he will do the same thing by offering a reward, then will try to play the pity and blame card if you ask him to deposit himself/herself once the message pops up.
hope you are now aware of this, stay safe and aware.