I heard someone mention this is possible on another thread.

I have had some books that have been sitting around unclaimed for several years.  The one that's been posted longest was posted on 7/7/2006 (six and a half years ago.)

When I am posting books, I would rather just take ones that are in oversupply on PBS and give them to Goodwill or the Salvation Army.

People have also told me that you can scan books you're thinking of listing and finding out immediately whether they are in oversupply or in demand.

Can you tell me how to do this?

If you put the book on your Reminder List, you can tell how many copies are in the system.  I posted a book awhile back, then realized there were already over 500 copies already posted...so yes, I deleted mine and donated it elsewhere.

Before you post anything search for the book. it's information page will tell you how many people are wishing for the book.

There is an app for Android phones called PBS Wishing that allows you to scan a book's bar code so you can see if anyone is wishing.  It's free and requires you to download a bar code scanner, also something you can get for free.  I use it all the time.  One thing I have noticed is that it is not always up-to-date, so if you scan a book and see only 1 wisher, that person may or may not still be looking for the book.  You can also just acccess PBS with your smart phone and type in the ISBN, but scanning is usually much quicker and easier.

Thanks to all of you.

I have an Iphone, not an Android, but at least now in the future I know how to check books for interest.  My hubby plans on doing some book dealing when he retires in December--books he deems "collectible" (and Lord knows he has plenty of those).  He sometimes will go to sales where books are $1 a bag and bring home a bag because he thinks one or two are "collectible."  I go through them and sometimes list ones I think would be in demand--now I can be more scientific about it.

I would prefer posting on PBS than bringing to a used bookstore because of the selection.

Maryanne, there's also an app for iOS - it's called BookSwap. It's made by a third party (as is the Android app, I believe) and is pretty minimal, but the nice thing about it for me is that it will scan barcodes using the phone camera and allow you to look up whether a book is wishlisted, add it to your wishlist or to your inventory, etc. Much faster than having to type a bunch of ISBNs in.

ETA: I also meant to say that I do similarly to what you described - I only list something if it is wishlisted or will be the only copy available. My storage space is limited and it's not worth it for me to wait for my copy of well-posted items to filter up the FIFO list - I simply donate those books to my local Friends of the Library or thrift store.