Absolutely employees make mistakes. Its how the business deals with those mistakes that matters. I wouldn't be happy with the way the business handled all this, YMMV.
I agree. How the business handles it is important.
And I will add, (and to be clear, I am in no way referring to the OP or to the business in question here) there are 3 sides to every story:
1) customers side,
2) business side,
3) facts...and lots of times they are not the same.
I deal with customers daily.
Some are very polite, and a pleasure to deal with.
Some are very aggressive, rude, abusive, you name it.
Sometimes the customers initial interaction influences how the issues get resolved/handled.
Sometimes there is nothing that can be done, and person is unhappy (ex - sold the last item, don't have any more to sell)
Sometimes there is lots that can be done (and is done) and person is still unhappy.
Every interaction is unique. There is no "one size fits all" solution.
Sometimes a business will do everything they can to try to keep your business.
Sometimes the customer is so high maintenance that the business doesn't care if they lose that customers business.
Everyone should work 6 months of retail. It will make you a better shopper.
EDIT - and sometimes, I should add, the employee is having a very bad day, for the same reasons we all have bad days, and unfortunately it resulted in a poor customer transaction/experience. It happens.