Absolutely! This is my number one flipping source. I comb three to five different Thrifts almost every day looking for books. If I can buy them and make at least 3X what I pay - I'll buy them.
There definitely is a technique to finding the books (knowing what to look for), and also for sorting them out to make sure that I am getting maximum returns from the book buying companies.
I have had many people tell me that selling through FBA or EBay I'll make more money - but I'm a lazy bastard and would rather sell to the various book buying companies as they are a known quantity and easy.
It is very hit and miss - last month I made $350 from one box of books I found and bought for $19. This month has been sorta dry with just a few $4, $2, books. I just pile them up and when I reach a critical mass sell them off.
I have make a couple of thousand dollars over the past few months.
How does it work?
When I go out to look for books I first look out for "USED" stickers which tell me that these books once had enough value to be sold.
Often these are full-on text books, or used in some university class. Text books are usually my best finds and have the most value. Condition matters, as do any supplements (CD's) - a beat-to-shit book, or one without the supplements is valueless.
After text books I look for esoteric books, something odd, or very specialized in nature. My $350 box of books were all books on hypnosis and NLP that obviously were from a therapist.
Most fiction is not worth anything, unless they are brand new, so I usually do not bother.
I also look for high-end publishers, Taschen, etc. although only certain titles are worth anything. I have found that some high-end cook books are sometimes worth checking.
I will scan the stacks, and grab out books and scan them with the Bookscouter app. Often text books will have stickers obscuring the bar code and you have to manually enter the ISBN. Sometimes there is no internet connection in the thrift and I have to grab the books, and take them to an area of the store that has a decent connection - I always take the books back to where I found them.
I usually use the 3x to 4x the cost of book rule, and will not hesitate to buy a book that will only return me a few bucks, as I can bundle them together.
Once I buy the books I take them home and then enter them again on the Bookscouter.com website. I then will start making piles of books, one pile for the highest price from each book buying site (I have accounts on about six or seven). Each site varies as to price paid, and so this way I can get maximum return. I will not hesitate to sell just one book to one site, and the rest to other sites if I can make more $. Each site has a minimum number for a sale, some as low as $5.
After I make my "maximum payment" piles, I submit my books to the respective sites, accept the offers, print out the free mailing labels and packing lists and put them on top of each respective pile. Then I get ready to pack them.
I re-use FedEx and UPS boxes that I nab from work for free. I also grab the clear, self-stick label envelopes from work, or from FedEx when I make a drop-off. I am also lucky enough to have an endless pile of used 24" X 36" rolled plans sitting in the recycling bin at work - I will grab a roll or two to use as packing material.
I turn the boxes inside-out and tape them up, pack up the books by wrapping them in the plans, and tape the crap out of the boxes. I put the packing slip and the free mailing labels in the clear envelopes, and then drop the packages off at the USPS, or FedEx on my way home.