Thus, signatures or notes by persons other than the author can be valuable too, provided that person is important. A book with notes in George Washington’s hand is bound to be of value, particularly if that book played a major role in his career.

Of course there’s another way to value your books, Mr. Gloss reminds his audience, and that’s to bring them to him. He can be found at the Brattle Book Shop, 9 West Street in Boston. If someone has a collection and lives near Boston, he is willing to pay them a visit. If they live in the Northeast, he may still visit, but will ask more questions first to ascertain whether the collection is likely to be important. It’s rare that he looks at collections located farther away, but once in awhile he will travel to other areas.

Mr. Gloss does note that the appraisals he gives are of the retail prices. The price which a bookseller can offer an owner is naturally going to be lower than the retail price as he needs to cover expenses and make a living. Mr. Gloss says that he buys most of his books for between one-third and two-thirds of the selling price. Low priced books require the largest margins to be worth the effort, while expensive books can be sold for lower margins. He cites an Audubon he bought for $100,000 and sold for $105,000. The margin was only 5%, but he points out that’s still $5,000.

How did Ken Gloss learn to appraise so many different books? He chalks it up to experience. “My father was in the business before me. I’ve done this all of my life. You do it and do it and do it.” He goes on to note “I’ve worked at the store since I was 5-years-old, though I doubt if I did much work then. Day in, day out, I’ve been doing this.” A few weeks ago he purchased an entire 5,000-volume library. He was able to value it in about an hour and a half because, he explains, it was a “consistent” library. He admits that he undoubtedly got the values on a few titles wrong, but that they balance out.

Mr. Gloss estimates that at road shows like the one this evening, he will have seen exactly the same copies of 85% of the books he is shown before. For another 14%, he will have seen something very similar. Once in awhile something will be new, and he will usually have this person call him the following day, so he can research the book through his bibliographic and other resources.