There is no grading scale here. There is a state, and then a short list of specifics, and the state has to be the first word in the title.
The state
Tested, working — you powered it on and used it. Tested, with faults — it runs and something is wrong. Say what. Untested — you did not power it on. Say why if there is a reason. For parts or repair — a known fault that stops normal use.
Never write "working" for a device you have not switched on. That one word is the difference between a sale and a return.
Then the specifics
Screen — scratches, dead pixels, burn-in, any delamination. Photograph on a white screen and a black one; different faults show on each. Battery — age, reported health if the device gives it, real-world life. Ports and buttons — every port tried, every button pressed. Say which you tested. Body — dents, scuffs, a bent corner, a cracked back. Repairs — screen, battery, anything opened. Who did it and when. Software state — signed out, reset, and what version it is on.
The sentence that should be in every listing
"Signed out of all accounts, removed from my account, and factory reset."
If it is not true, do not write it, and understand that the buyer may not be able to use the device at all. How to sell electronics.
Cosmetic grading words
If you use them — excellent, good, fair — define them in the same breath. They mean too many different things otherwise, and a buyer's "good" is rarely a seller's.
Questions people ask
How do I describe burn-in?
Photograph a grey screen and a white one. It shows on both and on neither in normal use, which is exactly why it needs showing.
Is "lightly used" a condition?
No, it is an impression. Say what the marks are and where.
What if a fault is intermittent?
Say it is intermittent, say how often, and price for it. Intermittent faults found by a buyer are the hardest arguments to settle.
More: condition words across every category, buying electronics.