The first question you should ask a plumber you plan on hiring is if they have the needed credentials and certificate to carry out plumbing work. You should also ask them if they have insurance coverage. This way, you are protected in case of any issues while they are working on your project.  You should also ask them if they have any experience handling the kind of plumbing issue you are facing. Also, make sure you ask them for their charges before agreeing to hire them. This way, you can avoid any issues after the work is done.