How do you determine the price of a used book? How much does the owner’s name written in the front decrease the price? How about highlighting? Does it matter how old the book is, like if it was published ten years ago? And so forth.
Check amazon, eBay, etc. for same or similar items. Most of these have guidelines (e.g. Amazon’s) for setting condition.
Out of print items sometimes have excessively inflated prices. The price people are asking may not reflect a value anyone sane is willing to pay.
It’s very straightforward: what the market will bear.
Do a search on the book, see what everyone else is charging, and base your asking price on that. Don’t forget to take shipping into consideration.
I recommend using bookfinder.com to research your pricing - Amazon’s marketshare isn’t as big as they want you to think it is, and bookfinder searches dozens of different sites.
The rule on damage/defacement is to disclose everything. If you don’t, you’ll end up with a pissed-off customer. A former owner’s name on the flyleaf has negligible effect on value. Highlighting has a dramatic effect. Many people won’t touch a book that’s been written in or highlighted. I have about 17,000 used books in my store (about 10% of them listed online), and I don’t accept any with highlighting at all.
Unfortunately, in the last ten years, the online used book market has changed from mostly booksellers who understand ratings, descriptions, and so forth to mostly people listing a handful of books super cheap to unload them. They’re poorly-described, you can’t tell when something’s a first edition, and prices are all over the map. As a buyer, you get something described as “fine condition” and find mold, damaged or missing dustjackets (that can knock half or more of the value of a book right there), book club editions sold as regular editions, and much more. It’s frustrating.
Agreed, for non-rare books. If you’ve got something that might be rare and this isn’t your main area of interest, you’ll probably be better off at least getting an appraisal from someone who specializes in that subject area, and possibly consigning the book for sale. See below for a few cases where even a good seller missed profit on a much more valuable book by not knowing the particular subject material.
Seconded. One thing to note is that some of the sellers bookfinder (I remember when it was mxbf) lists are actually brokers who mark up a book that you may also see listed by the real seller.
If it is a famous owner, it can increase the book’s value.
I’ve been both badly burned and pleasantly surprised due to omissions in a seller’s listing. Fortunately, I’ve mostly been burned on cheap stuff and surprised on valuable stuff. One of my purchases listed as “notes by previous owner on endpapers” turned out to have said “Copy 1 of 250 for my dear friend X’s collection of First Editions”. Another (first London edition of the Charles Davis Egyptian Book of the Dead - 1894) was described as “many notes penciled in margins” was actually Robert J Hubbard’s copy and comprise his commentary on the translation, as well as a start on translating parts not yet translated at the time.
On the other hand, this has brought things out of the woodwork that might never have been listed. Booksellers were always an odd bunch (no offense intended) - I remember going to various shops and requesting a book they had listed in a print catalog, and had them go “oh, we can’t find that one - if we find it we’ll call you” and not get a call for several years. And if I requested they search for a not-too-hard-to-find title, they usually wouldn’t bother. This was before mxbf, and there was a non-public listing service used by booksellers to share requests and listings.
Regarding things coming out of the woodwork, there have been some titles where there were only a few known copies extant, and I had one or more of them (in one case, there were 3 known copies of which I owned 2), came up as “not in NUC”, and yet I’ve seen at least 3 additional copies listed in recent years on bookfinder.
I use Alibris.com to sell books. It has a handy feature for beginners. After you enter the basic information about a book - publisher, edition, condition - you can click a link that brings up all the other copies of that title in order by similarity. You can then manipulate the results by price and other variables. You can also read the full descriptions entered for each copy to see exactly what flaws are listed - or not. That allows you to price your book for the market that will be interested in buying it. People who have to have a first edition are different from those who have to have the dust jacket are different from those who want a clean reading copy are different from those who want a signed perfect copy. You need to price the book accordingly.
As with every other field, you get better at pricing with practice. The first few times will feel extremely tentative. After you enter a hundred books of all kinds and conditions you’ll begin to develop a feel for what buyers look for and for the individual value of a book. Then if you want the book to sell, price it below the competition. 
Yes, this has elicited a race to the bottom. For any reasonably popular book on Alibris - which is just one of many listing services out there; I always start with bookfinder.com myself when I’m buying because it’s a meta-search site that searches all the important ones - the first 50 or so listings will be under a dollar. I don’t even bother listing any book for under a dollar. My storage space is limited and so is my time. The odds that I’ll sell a cheapo title are too small. Those books get donated to a library book sale.
Although bookselling is something that has become easy for amateurs, it is still a business and you are in competition with professional bookdealers and savvy collectors burning off their duplicates and excess. You have to treat it as a business. You’ll be disheartened to find that the niches are mostly filled for ordinary books. Most paperbacks will sell for less than the cost of mailing them out. So will most bestsellers, even if they are first edition hardbacks. Rarer books will have less competition, so they can be priced higher, but there are also fewer buyers for them. Condition is king. If you have a rare book in great condition you can make money. I bet you don’t. The spine ends will be “bumped” or curved in; the dust jacket will have tiny nicks and tears, pages will be dusted, spines will be creased. All those lower the price of books far more than an interior inscription. You’ll learn this after reading hundreds of descriptions.
Practice, practice, practice. That’s the only advice.
Thank you for the info. This is actually not for me, but for one of my clients. I told her I’d start a thread and share the responses. (She’s probably doing her own research right now, but I wanted to gather info just in case.)
What’s the deal with book club editions? Are they inferior in some way, or is this a perception thing?
They are inferior in a couple ways. To a collector they are simply not first editions. Part of the thrill of collecting is to have one of the first copies off the presses, and book clubs print tens or hundreds of thousands of copies. From a purely quality standpoint book club editions tend to be cheaply made and bound. The paper is of a lower quality, the binding is more likely to fall apart and leads to a less attractive book.
They often are physically smaller as well.
Even if they’re the same size, any experienced collector can tell a BCE (book club edition) just by picking it up. They’re that different.
Thank You, thank you, thank you.
Somebody finally gets this.
Did I say THANK YOU for recognizing this? 
Another thing is shipping. Offer several choices, when I buy a book I would rather wait and have pay less, I don’t mind waiting as long as I know it was shipped
Right, a name or even an inscription “To Bobby, love Grandma” doesn’t hurt other than rare collector items in great shape. Highlighting is a killer. So is a ex-library book, even if purchased legally.
As has been said- disclose everything. Other than an omnibus volume, or very very early BCE, they are nearly worthless, less than a paperback.
I’m a reader and a book collector, and nothing delights me more than opening up a used book and finding an inscription from the author, especially a well known one. I once found a copy of a mid-1960s baseball book with an inscription from the author to a well known NY Times sports writer, and tucked inside was a sheet of paper with the first paragraphs of a review typed on it, with hand written corrections.
Some of the folks who sell used books online never open them, and don’t notice the inscriptions. Either that or they don’t understand that a book signed by Kurt Vonnegut or Stephen Jay Gould should sell for more than $1.
Do ex-library books have the same quality problems as book club editions?
Ex-library books tend to actually be of higher quality than regular runs. The book is designed to withstand heavy usage. The problems with exlibs is that they almost always have that pocket where the “due by” card was inserted, or they have a scar where the pocket was removed, they have “Property of <Library>” stamps on them, and they generally have seen a great deal of use and abuse by the time the library weeds them out of its collection. Most exlibs have a lot of cosmetic flaws.
However, if I want a reading copy of a book, I’m happy with an exlib, if it’s in decent shape. By decent shape, I mean that the binding is still more or less intact and none of the pages are ripped or missing. I won’t pay a great deal of money for an exlib, though, unless I’m desperate to have it for a reference book.
Yes and no, mostly no.
There are library editions of books, such as Lynn describes. (Actually, today you’re more likely to find library editions of audio CDs or DVDs or other media sets that are packaged in flimsy cardboard that won’t hold up to any use.) However, in my experience, the overwhelming majority of library books are the exact same regular printing as those bought in bookstores. They’re just bought through a distributor, such as Baker & Taylor.
Special library editions cost more and libraries haven’t had decent book budgets for decades. They also haven’t had space for decades, so they no longer try to keep books forever. When they get old and nobody takes them out anymore they simply get tossed. No reason, therefore, to spend money on their lasting. And publishers see no reason to spend more money on a small print run.
So library editions are mostly reserved for classic novels or special reference books that are likely to be around for a very long time and be heavily used by schoolkids.
For The Da Vinci Code, conversely, a library will buy a dozen ordinary copies to keep up with demand and then whittle them down as they go bad.