A work permit is absolutely essential. Do not take up any job until and unless you have an authentic work visa or you are liable for a heavy fine if you were to get off easily. But most likely you will find yourself facing a term in jail.
Also if conducting a business please ensure that you have adequate funds in the bank before you issue a cheque, as a bounced cheque will not be taken lightly.
You will be slapped with a law suit and will have to face both civil and criminal charges. Even after your term in jail is completed, you cannot leave the country until and unless all your debts are cleared.