Your Law books look interesting however I don't think they are in much demand. Seeing as how you live in a different state than me I'll give you a few tips. I hunt the thrift stores quite often for books and have scored many off their shelves for pennies. My personal best thus far sold for over 250.00 on ebay (in somewhat rough shape too !)
Books are a specialty of their own. You definitely need to do your research if you want to spot the gems. First off stay away from any and all popular fiction. 95% of all the books I buy at thrift stores are non fiction. The only exception to this is 1st editions (you're going to need to know how to tell if it's really a first edition) by big name authors that are still in demand. I still buy any Harry Potter first I find these days but wouldn't touch a Daniel Steele because she went out of demand years ago. Or if it's an autographed copy (preferably a name you recognize). There are a very few titles out there in fiction that will fetch huge sums but you will need to research those. Generally they come from very famous authors who for one reason or another didn't sell many of that title. I'll give you an example here: "Cycle of the Werewolf" by Stephan King. It was one of his very early titles and not very good. It was also never printed in huge numbers (hard cover - 1985) and thus is an extremely rare and desirable one for his fans. I have only ever seen one and i got it for $2.00 at a rummage sale and sold it later on ebay for over 30.00 Another of his would be a true first edition of The Gunslinger which would be worth hundreds. There are also some genres of older fiction that will sell well such as 1950's juvenile literature, pre- 1960 LGB literature, but once again do some research to familiarize yourself with those.
Like i said I mostly buy non-fiction. Non fiction books are far more specialized and the more specialized the topic the more interested In it I am. Some legal books ( i normally only buy the finely bound ones) and some medical books are definitely good. I'd stay away from nursing or home health care yet jump on a neurosurgery book. I've scored big in such fields as leather working, wood decoy carving, metallurgy, spiritualism etc. The more esoteric the subject matter of the book the better. I normally avoid college texts unless they are less than 3 years old and even then I pre search them by ISBN online first. There are tons of websites that buy those and if they want it I know Ill get more on ebay.
Last couple of tips: Carry a smartphone with internet with you and start searching ISBN 's right there in the store. I use
BookFinder.com: Search for New & Used Books, Textbooks, Out-of-Print and Rare Books which allows you to search with or without a ISBN. Once again you need to learn how to sift through the results in order to match what you have. There is a huge difference in value between an original 1st edition Hard cover and a much later 1st edition reissue. For that matter there is a huge difference in an Ex Lib and a regular one as well. So do your homework !
I love to go to estate sales too ! It seems that every estate sale will have a shelf full of books and quite often there will be several (if not many) non fiction books. After all most older people buy books about their own personal hobbies and keep them for life. Don't hesitate to make an offer to who ever is in charge at the sale to buy the books in bulk. I once got 5 large boxes of books on metallurgy at an estate sale for $25.00 and made hundreds on ebay.
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