The rule of thumb for diesel is black smoke is oil and white is fuel, i.e. having white smoke check airways ,filters etc. Black smoke injectors, .piston rings ,valve guides etc. But all diesels smoke on start up, An old Foden lorry would fill the yard with smoke and if they soon clear they are O.K. Some engines are more prone to smoke than others. Get it up to operating temp and then check it. If you are not happy go to another diesel engineer and ask him to check it before you go back to vendor