Hi ya;
Yes, call me stoopit, but yes, I do tell the cashier about the price difference, 'cause you are right---it is all about integrity. If the situation was reversed--if the product was more than it was said to be out on the floor--I'd want to know.
I am very blessed that I don't need anything--or want anything--that badly that I would create bad self-karma; I do that unintentionally enough as it is

Ciao, Bella!
SeSo