Most, but not all, hardcovers come with a jacket of some sort. If its missing, it can greatly effect the value of the book. But not all books come with jackets and its sometimes hard to tell if it was issued with one or not. Recent books, the data from the publishers catalog should let you know if it was issued with one. But for older titles or ones by defunct publishers, you may need to look at similar listings to see if a jacket is mentioned or not. However, for more obscure titles, that’s not a sure bet just because there are far fewer examples out there. It may well have been issued with one but there are no copies for sale that have the original jacket.
If it’s pre1820, it didn’t have a jacket. Books in the 19th century may or may not have come with a jacket… but the jacket was often plain paper with only minimal lettering on it. They were often discarded by the bookseller themselves as the book bindings were illustrated while the jackets generally were not. They were really more like wrapping paper than the jackets we’re familiar with today. These types may or may not affect the value of the item, depending on the quality of the jacket. They will generally have a smaller effect on price than illustrated jackets from later periods. Some modern fiction can have incredible price variations depending on the presence of the jacket. A pristine early Hemingway with jacket would enable you to fill up your investment trusts quite nicely while the same book sans-jacket might only be worth a few hundred dollars.
Illustrated jackets that were meant to stay with the book after purchase became popular at the end of the nineteenth century and really took off in the 1920s. Some jackets from that period are more valuable than the books they covered!
Most modern hardcovers are issued with a jacket. Fiction books generally have unillustrated boards, so it’s glaringly obvious they’re meant to have a jacket. A missing jacket makes for a huge price difference here!
The exception to this is that some hardcovers in box sets will have no jacket. If the spine is very decorative but the boards are plain, you may be dealing with a box set that’s lost the box. A lost box is roughly equivalent to a lost jacket… so long as you have the other books that went in the box. If the rest of the set it missing, that’s a whole different problem!
Modern hardcover children’s books and nonfiction sometimes have an illustrated cover AND an illustrated jacket. Or sometimes just an illustrated cover and it was issued without a jacket. Books labeled as “permabound” or “library binding” generally are issued without jackets. If it has an illustrated cover, it may or may not have been issued with a jacket. A missing jacket is less of a concern with these because all the info and illustrations are still there, so may have a very minimal effect on pricing.
Paperbacks are very rarely issued with jackets. When they are issued, they are generally only in trade size books. The jacket generally has information both on the back (unlike hardcovers) and on both inside flaps. The paperback will generally have an illustrated cover, but little to nothing on the back. A missing jacket here isn’t as big a deal as a missing jacket on a fiction hardcover, but since some of the description is missing, it will lower the price some. These are pretty rare, so unless when you’re pricing the book you see mention of the jacket in other listings, don’t worry about it. The vast majority of paperbacks don’t have dust jackets.
Japanese books may come with an additional partial jacket called an Obi or “belly band”. These are generally between 1/4 to 1/3 the height and will include additional info about the product, related titles, and ordering info. These are on TOP of the regular jacket! They’re similar in function to the promotional stickers used on American books, but much more elaborate. How desirable the obi is varies wildly. A book with the jacket and the obi is definitely more valuable than one with just the jacket… but by how much is a big question. It really depends on what’s ON the obi. Since the obi doesn’t have a separate ISBN it can often be hard to tell how desirable it is if you can’t read Japanese. Assume it adds some value, but the price difference won’t be as great as the difference between the same book with a jacket and with no jacket. It’s about 99% complete with just the jacket and no obi. The obi just adds that little bit extra for collectors. If its a widely available book you’re pricing as a reading copy rather than a collectible, the presence of the obi or not shouldn’t greatly affect the price. You will occasionally find belly bands on books from other countries, but they’re sufficiently uncommon that you shouldn’t look for them on other types of books. It’s more likely that the book was not issued with one at all.
And the final consideration of pricing is where you’re going to sell it. For very common books with no jackets, it doesn’t really matter. The price difference between online and offline is so minimal as to be nonexistant. For rare items where there’s not a lot of copies around, it could go either way. A jacketless book is very unimpressive in person and is unlikely to sell to the casual browser. It may not be worthwhile putting out in a brick and mortar shop at all! It may only have value on line where people will be attracted to the description and contents rather than the cover illustration. so you may be able to price it higher than you would in a shop. Conversely if there’s not a lot of difference in price between one with a jacket and one without online, you may want to set a lower online price because the margin is so thin. You need a much bigger price gap to get people to buy it without the jacket. If its desirable but uncommon, you may then be able to price it higher in a brick and mortar just because people won’t be able to find a local copy with a jacket.
And should you find yourself in the position of having both one with a jacket and one without, don’t display both at the brick and mortar store! display the one with the jacket and list the other one online. If someone wants to haggle on price, offer to fetch the cheaper jacketless one from the back. They may well pounce on it at the original price, even though you’d have trouble selling it without the jacket if it was displated alone. That way its not taking up valuable display space but still has good odds of selling both online and in the store.