It’s ridiculous to think that people will be carrying around gem test kits.
Trade requires trust, but also verification for a basis. Assaying precious metals and grading stones are vital to establishing worth.
Many people already possess the kits. Most any semi-professional geologist will have them, and they don’t require consumables like assaying kits. Some old-school jewelers will have both assaying and grading kits.
Both skill sets would be a valuable asset for an isolated community.