How NOT to treat your customers

For the past day, I have been berating myself for not speaking up on this issue, but being shy, I didn't have the guts to say what needed to be said to the person at the time.
I went to a liquidation store, specifically to find a new blender, knowing I would need one today, since I had a root canal done this morning, and knew how sore my jaw would be from previous experience, plus I had read that it's best not to chew with a newly done tooth. Anyway....
I was lined up to pay and the following scene unfolded before me....
Man walks into the store, approaches cashier. Explains he had been in earlier, to return a calculator, and was told he had to have the receipt. Man had gone home, dug up said receipt, and driven back to the store. Man provides faulty calculator in original packaging with receipt. Cashier refuses to exchange it. Man tells cashier the manager said he could. Cashier calls manager, manager says yes, that is correct. Cashier slams down phone and starts berating customer, saying it's just a lousy $2 calculator, she shouldn't have to exchange it, etc. Man points out the calculator does not work, simply wants a replacement. Cashier starts on this huge tirade about how he should have brought it back 1-2 days after purchase, and says as far as she is concerned, she is in charge and doesn't have to do anything. Meanwhile there is a sign saying the store will happily exchange faulty items with receipt within 30 days. It had been about 20 days, I assume the man had been off on Christmas holidays, etc.
Man stalks off in hopes of finding the replacement calculator down another aisle. Cashier goes "Oh yeah, go off and cry over a lousy $2!". The other people in line are starting to get a little upset by this, and start taking the man's side. Cashier then starts arguing with each and every customer about it, and complaining to every customer about it who didn't say anything yet.
My opinion is such: This woman should be fired. This woman had no right to say the things she did, no right to treat a customer that way, no right to argue with a whole line of people, and certainly no right to be whining about it to everyone with ears as she went along. The man had every right to return the item for exchange, the sign was right there to say so, and maybe it was just a $2 calculator, but $2 is still $2.
If I'd had the guts to do what I wanted to do, I would have told her exactly what I thought of her behaviour, I would have demanded to talk to the manager, and I would have walked out, leaving my items right where I had stood, loudly declaring I would not buy from a store that would not only not follow its own return policies, but would heap on the verbal abuse as well.
But I am a chicken. Bock, bock. I meekly paid for my purchases, listened dumbly to her ramblings about the poor man, and left. The sad thing is that I had Daughter with me. No child should have had to listen to that kind of behaviour!