How to tell faux tanzanite from real....questions/help please!

Hello ladies....I have some questions.....who would I go see to truly verify if a gem is real or a good cz?

I know you can look inside of rings to check the stamps but in this case I was told by the original owner it is a real tanzanite....yet stamping inside of ring is sterling cz....it has clear cz's in the band/mounting and the larger main stone/gem is the tanzanite. I know you could have a jeweler put a real gem in a sterling cz mounting so it's not impossible...how can I tell?

I did not buy this online...it was inherited. Had the person not told me this about the ring I would have assumed it was faux based on stamps inside of ring.