I would say that the answer is "it depends". It depends on what your client expects you to deliver. In terms of photo quality, the 12MP camera is decent, but for serious work like inspections or mapping, you probably want to get something with a better camera.
Even though the Phantom 3 Professional/Advanced/4K still has a 12MP camera, the results are better. You also have to keep in mind that your competition will likely be packing drones with better cameras. If you can spare the investment, get the best camera you can.
Another problem is customer perception. A lot of clients see the Phantom series as toys, even though they're quite capable. I have had to explain more than once that my P4 Advanced has a 20MP camera on it that provides serious capabilities for mapping, and explain that it's not merely a toy. This could be something that pops up if you show up to a job with a lower end bird.
TLDR: Get the best drone you can. While the P3S has a decent camera, it may or may not get the job done. I wouldn't take it to a job, but that's just me.