Every antiquarian bookseller has had the same conversation. A customer writes to say the book "isn't as described", and when you look again at your own listing you see the problem at once: you wrote "some foxing to prelims" when what you meant was "six leaves heavily spotted". The book itself has not changed. Your description simply let the buyer imagine something better than what arrived.
Accurate condition reporting is not a courtesy tacked on at the end of a catalogue entry. It is part of the trade's machinery. It reduces returns, prevents arguments, and — perhaps counter-intuitively — helps good copies realise good prices, because buyers who trust a seller's eye will bid more freely on that seller's stock. Vagueness costs money. Precision earns it.
Damage to the binding should be described in the language binders actually use, because that language is compact and unambiguous. A few terms repay memorising.
Foxing is the most abused word in the trade. Strictly, it refers to the reddish-brown, usually irregular spotting caused by fungal activity and metal impurities in the paper, and it tends to be worst at the edges and in the gutter. If the marks are pale and even across the whole leaf, "toning" or "uniform browning" is more honest. If they are dark and clustered, say so, and say where.
Useful distinctions worth making explicit in a listing:
Marginalia deserves honesty too. "Occasional pencil notes, easily erased" is helpful. "Some annotation" is not — it might mean a signature on the title page or a scholar's quarrel with every paragraph.
Rebacked, recased, resewn, repaired — these words are often used loosely, and buyers notice. A reback means a new spine strip has been fitted, usually retaining the original backstrip where possible; "rebacked, original spine laid down" tells the buyer they still get the gilt and the lettering they want. A recase means the text block was reattached to the original boards. A resewn book has new sewing; its gutter margins may be narrower as a result.
The single most useful thing you can add is a note on reversibility. Conservation-minded buyers will accept sympathetic repair with reversible materials far more readily than they will accept a trimmed, washed and rebound copy. Say if plates are guarded, if a title page is supplied in facsimile, if endpapers are renewed. Silence on these points is what turns a routine enquiry into a refund.
Specificity is your friend. "Tear to margin of pp. 84–85, approximately 4 cm, no loss to text" beats "minor tear" every time. Give page numbers, give measurements in centimetres, and give a position — upper fore-corner, lower gutter, head of spine. For bindings, describe wear clockwise or by panel: "rubbing to extremities, most pronounced at the tail of the upper joint".
Date your observations. A catalogue entry written in March may be read in September, and a note such as "joints sound at time of cataloguing" is both truthful and useful.
Before you write, work through the book physically in a fixed order: covers, joints, hinges, endpapers, title and prelims, the body of the text, plates, and the rear matter. Handle it in good light with the spine gently flexed. Then write the description in the same order, so nothing gets skipped.
Where a flaw is serious, lead with it rather than burying it. Where it is trivial, state it anyway. The buyers who understand the trade — and they are the ones who will pay properly — are not looking for perfect copies. They are looking for sellers whose descriptions they can rely on without opening the parcel in a state of anxiety.