This is always an issue, but you can start by asking around your friends and relatives to see if they have had similar work done and what their experience was. You can also check on the web for local contractors and then visit their websites to see if they show examples of similar work, if they look professional, or visit their offices. Accreditations are always a useful indicator; look out for Health and Safety accreditations; you wouldn’t like to employ a company with poor safety standards. ISO 9001 is an industry-recognised office management accreditation that is audited externally to show that a company is managing its office to a high standard of competency. Is the builder/company accessible? Do you know where he lives or where the office is, and is the contact detail easily contactable and local? Is the builder/company fully insured for damage to your property or persons whilst carrying out the work?