When you put bookshelves for sale, the customers just buy individual books. Is there a way I can change that? Either a bookshelf that sells as an entire shelf (even if it doesn't work as a bookshelf at home, and I'll just use it as a "marker"), or a mod that changes how the items are sold? TIA :lovestruc

Well, normally, when you buy a bookcase, bookshelf..there are no books in it..right?
Bookcases are sold in furniture stores, and books in book stores (or library, depending where you live)
There are empty bookcases for download. You could find some, but this is not what you want, as it probably just sells individual books.
Some of them have just been emptied to get rid of the books, but still function as a bookcase, only difference, now you can put deco items where the books were.

What you need is any object that uses a bookcase mesh without a bookcase interaction..Oh boy, am I helpful.

Empty bookcases http://modthesims.info/d/463194
Then there is Anoeska's bookcases from TSR which are just a group of books that work as a bookcase.

I'm not sure exactly what you are after.

She wants to sell the bookcases as furniture items in a shop, not sell the individual books out of a bookcase as in a bookshop.

I think the only option is a deco bookcase. Or you could just look at your sims who bought books, think "Oh, they must have bought a bookcase" and delete the book and buy them a bookcase.

Those empty bookcases are perfect! I totally didn't think of that (I have a toddler with a stomach bug. That's my excuse and I'm sticking to it!)

But, yes, this is for my BACC and I just want somewhere where my playables can buy bookshelves, since I want to gradually move away from buying items out of the catalogue.
Using books as a marker is a good idea too, and what I've been doing.

So thank you!