Is this the American tourist's fault or the Chinese person's fault?

none of your aunt's fault... and a lot of fault of the cashier lady... but you must understand... this is no isolated incident... i too have a story almost similar... i came from Ukraine to work as an Escort girl in Shanghai... i could barely speak Chinese... while going for shopping i would ask my Chinese colleagues to help me in bargaining... initially they were very helpful... but then they tried to avoid accompanying me during my shopping sprees... when i asked, they said shopkeepers called them names in Chinese... coz as long as they helped me in my shopping, shopkeepers could not cheat me... you are still more vulnerable if you are all alone... if you touch a thing... or show your interest... they will force you to buy... they have no qualms about using means: good or bad... don't be surprised... take a lesson... coz Chinese are hard sellers... even adopting unethical means... in our place a shopkeeper can hardly get away with this... but China is "everything goes" society...

Salespeople can and will say whatever they want... but the slapping was unexcusable.

Your Aunt is being rude in the cashier's eyes, as the cashier lose business means she has no earnings or no food for home, which is a big issue there. It's sad that the cashier's reaction gone crazy as she hurts your aunt. I hope your aunt is ok. In Chinese culture, even they know the other store is selling at cheaper price, they don't say it in the store but you can directly tell the cashier that you found another good deal somewhere else and bargain for a discount in mainland China. In American eyes this is a fair trade world, no one is hungry as there are a lot of help and charity, but in mainland China, if they couldn't earn enough money for their big family, means no food and no one could help. That's why a lot of low income residents in mainland China would love to live in the United States. I hope this is able to explain why the cashier's reaction is so outrageous. As long as the cashier lady is the one hurting people, she is the one in fault whatever.

I think if she had said it was ugly or "cheap" in terms of fabrication, yes. But all she said was save your money. That's a free-market economy, that's not rude. I can't believe she slapped your aunt! She needs to lower her prices to be more competitive and not rip off American tourists. Whether rude or not, it would preferrably be something said quietly.

cashier lady came out and slapped my Aunt on the back really hard... aha, then Aunty calls the friend policeman who gives many bruises to the shop lady in return... very realistic but for one but... Aunty was speaking English while very few of shop assistance in China can hear more than "hello" in any language but Chinese... not mentioning such cool phrase as "stupid girl"... and the main point of lical trade -- here it's forbidden even to scare (even to scare) any of the foreign customers and toursts... coz if the foreign tourists will be scared (not even beaten) they will stop bringing their money to China... and no one will refuse a bunch of dollars for the swift pleasure of slapping someone's back... btw you aren't acting as a real American... where's the link to her blog with the pictures of the shop, its address and big letters: "this is the place where i was physically abused..." otherwise it looks like she's never been to China at all...

Whatever the cashier started, your aunt should have finished. However, is your aunt some sort of cheapskate? How much more cheaper would it have been back home?