The way I do these kinds of things is by using the Savvy Seller items from Midnight Hollow. The game won't technically recognize that I own the business, but I give my Sim some kind of open-hours, non-rabbithole job, and send them to man the register. I check the total sales at the end of the day by clicking on the register and use the familyfunds cheat to add that amount to my household. I also use the familyfunds cheat to "purchase" the property if I want them to own it. This way there's no requirement for upgrading. For a bookstore, the sims would be buying the bookcases rather than the books themselves, however the bookcases would still be there, so you wouldn't need to keep replacing them. Also, it's possible to have both the Savvy Seller register and the WA book register in the same building. I don't know when or if you will get back to this project, but I thought I'd share my strategies just the same. Take care.