Nobody grades an antique on a scale, and anybody offering to is selling something other than expertise.
The four words
Original — as made, with age and wear. The wear is evidence rather than a fault. Repaired — something broke and was mended. Say what, where, and whether it shows. Restored — work done to return the piece toward its original appearance: refinishing, retouching, replaced veneer, rewiring. Always declared, because good restoration is designed not to be visible. Married — assembled from parts of more than one original piece. Common, legitimate when declared, and one of the most serious misdescriptions there is when not.
To those add replaced parts, each named: handles, hinges, glass, feet, upholstery, movement.
Patina is not dirt
The surface a piece has acquired is usually part of its value. Removing it is not restoring it. If you have cleaned, polished or refinished anything, that belongs in the description as clearly as a crack. Common mistakes.
What to state, in order
What it is as far as you know · measurements in centimetres · original, repaired, restored or married · replaced parts · damage — chips, cracks, losses, woodworm, water damage · whether it is structurally sound and usable now · what you have done to it.
A listing with those seven is almost impossible to dispute.
Why no scale works
Because two pieces at the same "condition" can be a century apart in what has been done to them, and the thing a buyer is paying for is the history rather than the surface.
Questions people ask
Is woodworm a disclosure or a grade?
A disclosure. Say whether it is old and inactive or current.
Does an old repair lower value?
Less than a hidden one does.
Is "antique" a condition word?
No. It is a claim about age you should be able to support.
More: describing antiques, what one is worth.