Plumbers need licenses and insurance, so you should ask a company who is the responsible master plumber with the business, obtain a license number and ask for proof of insurance.
Ask for an estimate of the cost and a written contract before you authorize any work. Be sure to read and understand the contract. It’s a good rule to ask for estimates from three contractors for any major repair.
BBB Business Reviews are available 24 hours a day at bbb.org. The reviews list information such as the length of time a company has been in business, contact information and the company’s website if it has one. If a consumer has filed a complaint with BBB, the review also should show how the company responded.
BBB also has a list of tips on hiring contractors of all kinds.