Is Your Licensing Up to Date?
Many people assume as a courtesy that a plumber is licensed, but this isn't always the case. Some people offer their services despite lacking proper licensing or failing to update their license with a local agency. The risk you take in working with an unlicensed plumber is that their work may not be up to code. Since you chose to work with them, you may be liable for any deficiencies in their work. Not to mention the risks involved in trusting your home to someone without the proper qualifications! So always ask a plumber for proof that their licensing is up-to-date, and if they refuse, look elsewhere.
Are You Doing the Work?
This question ties into the first one; sometimes, a master plumber will rely on a team of laborers. While it's fine for a licensed plumber to have assistance from laborers, work on water and electrical systems must be only performed by experts. A plumber having up-to-date licensing won't do you any good if he's delegating these important tasks to people who aren't! Ask the plumber who provides your price estimate and displays his credentials if he's doing the work, and if he isn't, inquire about the experience and licensing of the plumber who is. If the plumber cannot provide accurate, detailed answers to these questions, then look for a different plumber.
What Will This Cost?
While many plumbers will provide a free estimate before performing a job, this is not binding. Contracts often include clauses that the property owner will pay for any expenses necessary to complete the job. This could mean that when the plumber needs to buy extra materials or spend more time than expected to complete the job, you'll be left footing the bill. This doesn't necessarily mean the services aren't worth it, but you should always make sure you have a good idea of what the job will cost. Ask if the charge is a flat rate, or a flat rate plus an hourly fee and what the estimate includes. Additionally, you should make sure you can get a list of materials used. This way, you can double-check with a local department store and ask if everything adds up. You should also request an estimate from three or more plumbers and see if they all match up or if one is suspiciously higher or lower than the others.
What Guarantees Do You Offer?
An important sign that a plumber believes in their work is whether or not they offer guarantees. The most confident plumbers will provide a written guarantee that they'll return and fix anything they've worked on in the next year or so. Others offer more specific, limited guarantees. This shouldn't necessarily be a deal-breaker, so long as you find their terms fair. However, you should not rely on any plumber who refuses to give any written guarantees of this sort.