A few things to consider.

Style - you're going to get some specific fashions and styles in some places and not in others

Quality of manufacture

Reputation. That's what branding is all about and why premium brands attract and can command premium prices.

Bargaining? Probably any small independent jeweller. Less likely at van Cleef & Arpels (or whoever), Tiffany, etc. Then again, if you buy "enough", you could ask the manager for a break in prices.

That's a systematic approach I'd use, not that I have any interest in jewellery.