A lot of times, a plumber has a choice on what kind of parts to use on a job. In some cases, the plumber might opt for the less expensive version, like maybe PVC pipe instead of copper. While this ultimately means a cost-cutting measure for you, it might not be the right move in the long run. If you want top-quality parts and you won't balk at the bill, then you should request a discussion when it comes time to order them. It's not so different from dealing with an auto mechanic. Sometimes cheaper parts make the job easier and more profitable for the repairman, but it's your own interests that matter most.