There are many such clues to extra-textual information in a book I have been treating this week: Archaeologia graeca: or, the antiquities of Greece, by John Potter, published in London, 1764. The book is an octavo covered in finely sprinkled, tan calf. Its decoration is modest but attractive, with a double-fillet, gold-tooled border on both boards and accenting each raised band on the spine. The boards have been laced on with three of the five sewing cords.
Inside the front board (cover), the acidic leather has burned the paper of the paste-down, making visible an imperfection from the leather-manufacturing process which would originally have been hidden on the turn-in, under the paste-down, when the book was newly bound [see white arrow in image above]. This gross imperfection in the leather is one indication that the binding is not of the best quality, and therefore may not have been a bespoke binding, which would have been bought in sheets and bound to the taste of an individual customer. The more closely I examined the materials, the more I saw signs that the materials themselves were not the finest quality, and the binding construction also showed signs of shortcuts. The high acidity of the leather suggests a quickly-produced product of inferior quality, further supported by the imperfection on the turn-in, which would have made this a "second-quality" skin. The textblock is constructed from handmade, laid paper which is coarse, has an uneven pulp distribution when examined in transmitted light, and shows no watermark -- all signs of a lesser quality paper in the mid-18th century.
The binding has abbreviated sewing (two-on), a less sturdy but faster-to-produce sewn structure than all-along sewing. The endpapers are not of any special paper stock; the pastedowns and fly leaves are the first two and last two leaves of the first and last textblock gatherings, respectively. So, while some care has been taken to make the book appealing to the eye (sprinkled leather, gold tooling, red skiver label), the craftsmanship evidence here strongly suggests this book was a trade binding, marketed ready-bound by the publisher to customers of lesser financial means, (perhaps even a student!)