My interpretation of these terms would be:
- Mint in Box means the yoyo comes with its original packaging (usually a box) and is indistinguishable in all ways from a yoyo that’s never been removed from said packaging.
- Practically never used means the yoyo was played so minimally as to be indistinguishable from MIB, but was played nonetheless. This is simply a nod towards full disclosure.
- NMTBS means the seller has not examined the yoyo closely/carefully enough to verify whether it qualifies as “mint” (i.e., indistinguishable from “new, unopened”) or not. Usually this is used to cover one’s butt in the event a buyer’s personal grading system doesn’t perfectly match one’s own.
Since, as far as I know, there is no official yoyo grading system, everyone is left to their own terminology and interpretations of such. Consequently, nobody is using misleading labels, per se, they are simply using labels that match their headcanon.