Still a shitty thing to do though.
There are so many reasons why this kind of behavior is toxic... If the intention was to keep the books, but for some reason they decided to return it, that's fine. Even buying thinking you might end up having to return it is still fine, mostly. However, buying with the sole purpose of lending for free, especially from a small business, is awful.
Geez. It seems you've no idea how a business is run.
I just disagree with the framing of “this one order was a third of our rent and it turned out fake”, like yeah of course they’re upset, but since it was fake to begin with, that wasn’t ever money they had, so they’d have to cover their rent somehow anyway. It’s a bit like counting piracy as a lost sale when the person was never going to buy to begin with. Of course the whole thing did work out in their favour in the end so cool.
Maybe, as someone else pointed out, they ordered replacement copies of the sold books unnecessarily.
Maybe they made accounting decisions (employee bonuses, debt/supplier payments, etc) based on their assumed revenue that month, and now they have to deal with an unexpected shortfall?
So many potential reasons why this isn't "zero effect".
Not sure why you're trying so hard to talk away the impact of the "shitty move by the buyer" here.
Im really not trying hard to do that.