We found a leaking bathtub at this house in Cumming using our infrared camera (see thermal image #1). The sellers hired a plumber who claimed to have fixed the issue. We were then brought back out to reinspect, and guess what? It was still leaking (thermal image 2).
The best way a plumber should troubleshoot similar leaks is to cut out the drywall and see where the water is coming from. Beyond that, they are just guessing.