To choose a plumbing contractor, ask the people you know for recommendations or look for contractors in the Yellow Pages, then interview the candidates personally to find out everything you can about their services (including costs and warranties), and ask them for for references. Before finalizing a choice, make sure that the contractor has liability and workman's compensation insurance. Check as well to see if they are members of any trade organizations, as this can help to ensure that they are aware of the most current regulations.
You should always expect a good plumber to find the problem, explain what caused it and what needs to be done to fix it. A professional should also explain everything once the work has been completed. Make sure that you understand everything and ask for clarification if you aren't familiar with some words.
Reliable professionals always use drop sheets or other materials to make sure that the surrounding areas don't get damaged. Once a plumber is done, make sure that you receive all information about the warranty and guarantees for the job, including cases in which the warranty might be voided.
When you receive a price estimate from the plumbing contractor, make sure to ask them what is included in the price and which services might cost extra. The flat rate pricing usually includes all the services and doesn't depend on the amount of time it takes to complete the job.