This Store Owner is blowing smoke... not a chance at this time for him to bring any
legal action against the client... How is he going to claim he lost business due to
your actions... total opinions here... do not lose one bit of sleep!!

What do you mean the store owner is blowing smoke ?
Unless I missed something or misread something, the store owner never said anything about legal action.

And in all likelihood, he won't, even though he may have a decent case. What business owner in a community like ours wants a reputation for suing his clients when something goes wrong? But if I were the OP, I wouldn't push him any further---if the original story is accurate, he may have some self-control issues, so why poke the bear?

A shop owner who sues a customer is not really thinking about his long term business life...BUT if you push him/her to far it could happen. Here are some articles telling you what "can" happen even its its simply a bad review of say a restaurant. There are plently more examples.....

Blogger beware: Postings can lead to lawsuits - latimes

Negative Online Reviews: Why You Can Be Sued for Defamation | TIME.com

I think the first tip-off to something fishy is the o.p. saying they saw the stone was cracked "and glued".

No jeweler in an established retail business is going to glue a gemstone. It's just absurd.

I don't even think the kiosk trinket vendors at Market Nights on the squares would glue a "gemstone".

Just my opinion.