I had a lot of books on my shelf that had been posted for a long time & not requested.   After hubby's nagging & threats to throw them out I decided to donate a bunch (67) to the local library.  Some had been posted since 2013 or even 2011.

Question:  How Long do you keep books on your shelf before your get rid of them?

Generally a year. Though I did have a few odd ball ones that have been on there 2 years.  I tend to post items that are either wish listed (because I finished them or found them at the library sale) or items with no more than 2 or 3 copies in the system. I'm able to cherry pick because I do have the book sale to get new books from easily, 2 times a year. They cost 10 cents to 50 cents a book.

I generally don't keep more than 100 books on my shelf either. Enough to keep the credits coming in but not so that I build up a huge amount. Of course, I also know that if I need to get more credits, just be sure to buy wish listed items at the book sale.

I decided at one point that I would not have more than one box on my posted bookshelf. I'll go through my box once or twice a year, right before the library FOL sale. I'll run a deal, then donate a bunch to FOL for the tax credit. 

Right now my shelf is almost empty. I'm only posting wish listed books.

I've found it really helps me to print out my posted bookshelf and check it against the actual shelf. I have had deal books that I've forgot to remove. I now use the "Mail Book to a Friend" for deal books.

I don't really have much storage space so I recently took off all my books except books that only have 5 or less copies in the system,and  I've only been posting WL books.    So , I guess I'll see how long it takes for them to be ordered and go from there.

Sorry its not much of an answer .but right now my small bookshelf has only 7 books and 4 of them are only copies.