Here is a partial checklist to start with –
1. Evaluate what plumbing service(s) you are seeking.
2. Verify their credentials.
3. Take a look at reviews.
4. Secure a contract of expectations from the plumber.
That is a good start. When you need a plumber in the Philadelphia area, particularly in surrounding Bucks and Montgomery Counties, call Joe Canty of All Drains Plumbing Bensalem. This is a guy that you will probably call over and over again for your plumbing needs. Call Joe at 267-356-3857. See some of his plumbing skills at alldrainsbensalem.com.