Checking the accounting data
This is the first thing to do is check the qualifications and certificates of the service engineer with whom you are associated. Regardless of whether they are a roofer, a plumber, an electrician, an artist / decorator, a carpenter or a gas master, if they are good, they would go through appropriate tests and pass the exams specified in the profession they chosen. Real professionals of service professions will have one or more qualifications related to the craft they have chosen.