I didn't quite understand if you are in Mauritius or not. Never believe an agent until you have tangible proof. Get the notary to show you a certificate that there is no lien then consider buying it. You will get the land owner's name on it too.
A deposit of how much is the notary asking for? If more than Rs1000 then he's a vulture.
You can buy with bank transfer. But do check what I told you above.
For the construction, check whether the land is agricultural or residential. If it's agricultural, check whether it is within the "irrigation zone" set by the government as you cannot build anything on this type of land. If residential, make sure no one will have a complain against your building permit by checking the laws of the type of building you are going to erect.
Hope this helps.