A cavity is just a hole or groove of various depth. It's probably less that one dentist sees a cavity and the other sees nothing and more that one dentist sees a cavity worth addressing the the other sees the beginning of a cavity that they figure will need to be addressed eventually, but there's not a major reason to do it now rather than next year or the year after that.
Also, I imagine some dentists might decide for their patients benefit (as long as there's no pain reported) to let a couple develop to a level is there's a few in various stages of development, so they can do them all at once with a single procedure.
I don't know how likely or accurate those are, but those are some of the obvious ways that came to mind that dentists might be seeing the same thing and suggesting different actions that don't boil down to them wanting to fleece a customer.
Also, I imagine some dentists might decide for their patients benefit (as long as there's no pain reported) to let a couple develop to a level is there's a few in various stages of development, so they can do them all at once with a single procedure.
I don't know how likely or accurate those are, but those are some of the obvious ways that came to mind that dentists might be seeing the same thing and suggesting different actions that don't boil down to them wanting to fleece a customer.