More prongs is better if you expect the ring to get banged around a bit, simply because its safer - prongs get bent, but more prongs means much less chance of losing the stone.

But, nothing is stopping a jeweler from putting a really expensive stone in a setting with few prongs.

As far as spotting a fake, a jeweler can do it. They use their loupe, that’s the small magnifying glass thing, and with 10x magnification, they can tell if its real, or CZ, or a piece of glass.

This does get more complicated if you want to also differentiate manufactured diamonds, becase that technology has been improving a lot over the last several years.