My dentist does the same. When I first went there (after not having gone do the dentist for 3-4 years, because I never had any issues with cavities) he told me that there are 4 cavities I need to get fixed. I was very sceptical at first, but agreed to get them done.

He fixed all 4 of them in 20 minutes. When he drilled open one of the teeth, he showed me how it looked with one of these small cameras that you could see live on the screen. It was absolutely obvious that there was a considerable cavity.

Explaining to your customers what needs to be done, proving it with pictures and/or x-rays, and explaining the different options generates a lot of trust.