Be sure that the plumbing company is licensed and insured. The license is a sign that the company has met state requirements and New York City for training. If the company or plumber is not insured than you may end up having to pay for any damage they might cause.
If possible get references and be sure to ask the following, very important questions. How long has the plumber been in business? What is his/her specialty? What guarantees does the plumber offer? How much experience does the plumber have with your type of project?
When selecting a plumbing contractor, you should also check with the town to be sure that the contractor's license is current. You can also check with the Better Business Bureau to see if any complaints have been filed against the contractor.
In emergency situations, choose a company that has a person answering the phone instead of a machine. You will be able to ask questions about the service and be able to ask for the approximate arrival time of the plumber.
Request a written estimate as well as a timeline for completing the job. An experienced plumber should be able to tell you what replacement parts are neccessary and inform you about your options in parts and repairs.