If a cashier ever gave me a hard time about any purchase, I'd ask to see the manager immediately, and demand that he/she apologize right there in front of the customers.
I did make a stink about not finding the book at first. The gal said they had 10 copies and went back to look for them. She didn't even bother to look out front.
She seemed confused when she couldn't locate them. I mentioned that I had noticed conservative books often were hidden in wrong sections. She seemed nervous with me for talking about such a thing.
As a began to leave I found Unfit on the table with all the other titles.
The check out guy was the snooty one. I was just glad I had my book and ignored him and wished him a great day.
Harrrrumph!