3) After receiving the money, will it be hard to convert my money to fiat on my bank account?
4) What are the withdrawal limits and exchange fees?
^If we are only talking about Bitcoin payments here and being able to liquidate it after, you wouldn't have any problems with it as long as your country has labeled legal to be traded/own and you have buyers for that Bitcoin or you have 3rd party wallets that can convert it directly to cash then you will have that cash in no time.
1) Is this method safe and the site reliable?
2) Can this be part of a scam and if yes, how?
However on this one where the buyer ask you to sign up on something or they will be the one introducing you to the escrow this will be a common red flag in any scam transaction out there. Bitcoin wallets should be coming from your own choosing as well as an escrow that is trusted or at least neutral to both parties. Them controlling the escrow part or what kind of wallet you have only means a scam will just go down in your transaction.