Start with the Spine, the Book's Backbone

The spine carries more weight than any other part of a book, and it usually shows the wear first. Close the book and sight along the length of the spine from the tail. It should be straight and square. A spine that leans to one side — collectors call it cocked or rolled — is common in thick paperbacks that have been read once too often, and it is very difficult to correct. Look closely at the head and tail, the top and bottom of the spine, where bumping, chipping and fraying appear first. On hardbacks, the cloth or paper covering often rubs through at the corners of the boards. Then open the book near the middle and watch the spine. A covering that bows away from the text block, leaving a soft gap, has a hollow back. A little hollowing is normal in an old book; a spine that has come away completely will not survive much more handling.

Hinges, Joints and the Test of Opening

Open the front cover and examine the inner hinge, the fold of paper where the cover meets the pages. It should be intact, with no split beginning at the head or tail. Even a short crack will lengthen every time the book is opened, so it is worth checking now rather than discovering next winter. The outer joint — the groove running down the side of the spine where the board meets it — should feel firm. If it flexes under your thumb, or shows a line of white cloth or thread, the board is working loose. On paperbacks, look for a hard crease down the spine and a split where the cover meets the first page. Finally, ask to see the book opened at two or three different places. A text block that cracks sharply, or shows a gap between gatherings in the gutter, is separating, and no amount of gentle reading will reverse that.

Read the Page Edges and the Paper Itself

The three edges — top, fore-edge and bottom — tell you a great deal about how a book has been stored. Foxing shows as small brown speckles, most often on older paper kept somewhere slightly damp. Light foxing is cosmetic; heavy, clustered foxing usually means moisture has been at work. Tanning, the warm browning of ageing paper, is entirely normal. Be more cautious with cheap twentieth-century paper that has gone dark and brittle, because the corners may crumble as you turn them. Water damage leaves tide lines, wavy or cockled pages, and often a musty smell. You may also spot a remainder mark, a felt-tip line or stamp on the bottom edge, which affects value but not reading. Ex-library stamps and withdrawn labels are similar: ugly, harmless, sometimes a bargain.

Imperfections You Can Happily Live With

A reading copy is not a collector's copy, and holding out for perfection is an expensive hobby. These are the flaws I would accept without a second thought:

• A creased, faded or slightly rolled spine from honest, repeated reading.
• Light foxing or tanned edges, provided the pages are sound and supple.
• A neat previous owner's name, a gift inscription or a small bookplate.
• Bumped corners, scuffed boards and minor shelf wear.
• A price-clipped dust jacket, or a jacket with small nicks and rubbed edges.
• A slightly loose first gathering that still holds firmly when the book is opened.

None of these will interrupt your reading, and each one usually knocks something off the price.

Faults That Should Give You Pause

Some damage does not stay put, and some makes a book unpleasant to handle. Be willing to walk away from these:

• Active mould or mildew. The smell spreads to other books on the shelf and is very hard to shift.
• A split text block. Pages detaching in sections, or a book that falls open at the same place every time.
• Missing pages, plates or maps, however cheap the book is.
• Heavy water damage, with stained, wavy pages and a damp, sour smell.
• Brittle paper that cracks or flakes at the corners when turned.
• Insect damage, which appears as small holes and fine dust in the gutter or under the boards.
• Strong smoke or pet odour, which lingers for years and rarely fades completely.

Small Habits That Save Regret

Before you hand over your money, do four things. Smell the book — paper should smell faintly of dust and paper, never of damp cellars. Hold it up and look along the top edge for a straight, level text block. Gently let it fall open in your hands; a book that flops apart in the middle is telling you something. And ask about returns, which most second-hand sellers will happily offer on a cheap paperback. If you are buying online, request photographs of the spine, the hinges and the page edges before committing, and read the condition description twice. A good reading copy should feel comfortable, not fragile: it should open easily, sit flat in your hands and invite you to settle into a chair. That, more than any stamp or signature, is what makes a second-hand book worth bringing home.