One of the main things you must ask before hiring a plumber is if he or she is certified, insured, and licensed by their state. If the state you live in doesn’t require licensing, you can still research to see if any complaints have been issued against the contractor.

While there might be exceptions to the rule, it is usually a good idea to be sure a plumber has been in business for some time. The more experience a plumber has, the more liable he or she is to get the work done right the first time.

Before hiring a plumber, you should always ask for estimates. Be cautious though since cost is sometimes linked with quality of work. This means that you shouldn’t use a plumber just because their cost is the lowest for a specific service. On the other hand, you must always make sure that a plumber’s cost is fair before hiring.

It is always a solid idea to ask a plumbing contractor for references prior to hiring. Reputable plumbers don’t have any issue giving you good references. Don’t be scared to ask.

The best plumbers usually provide some sort of guarantee on the work they do. Before hiring a plumber, ask them what sort of warranty they provide and be sure they are willing to stand behind their workmanship.

This seems like it should be obvious, but some plumbing businesses don't clean up when they're done, leaving you with boxes and old parts. 

Always inquire if cleanup is included as part of the cost and if not, why. Some businesses might charge for cleanup in addition to finishing a job, and the cost might be worth it. But again, don’t be scared to ask.