I looked all over their website and couldn't find what specifically is "guaranteed," other than "grading and authenticity."
Note that they use the word "guaranty" in their name, instead of "guarantee:"
https://abovethelaw.com/career-file...nd-guaranty/Which I take this usage to mean that, as it is used as a noun, it is just a thing, like a piece of paper for example.
If they had used "guarantee" though, then it's a noun and a verb: some action would (presumably) take place, like refunding money if their certificate was incorrect, for example.
Interesting...
Jim