I might not buy a diamond at those stores because of all the variables that go into appraising their worth, but would a ruby, because the dark color of the ruby makes flaws less visible.
Gold is gold, stamped with the carat, so unless a store is slipping fakes in, a risky operation for Zayles and Kays, it's not a worry. Gold being soft, I'd buy 14K. Not GF (gold filled) nor GP (gold plated).
Of course any gem purchase matters for it's resale and insurance value, so even if you can't see flaws, you want to know about them.
Tell him to ask for a written list of each aspect of the ruby's rating, and the weight of the gem apart from the weight of the gold.
Here's a good guide to rubies: A Buyerâ€™s Guide to Ruby Qualities: Natural AAA vs AA vs A - Diamondere Blog
Also, it's worth bargaining at any jewelry store!
I'd plan a day or even two going from store to store, taking notes, gathering WRITTEN info they write, letting them know you are shopping around, and armed with good knowledge.
I've found some good deals on ebay, especially pawn shops.
Here's $700-1000, US only, yellow gold and ruby, sorted by time ending soonest. ruby 14K ring | eBay