Employees seemed somewhat happy too.
They pay legitimately good wages for the markets they are in. However, they also know they are paying good wages, so they make the employees earn every single penny. I understand that it's more stressful and tiring than an average retail job, but as Don Draper would say, "That's what the money's for!" In reality, it almost certainly depends on the individual managers and whether the store is hitting targets.

Yes, but they also extract every penny of value from them. Minimum legal time for breaks, no visible tattoos, cell phones turned off, and broad manager discretion about things like having a stool at checkout. Apparently they are very upfront about it in interviews, at least, but they know they're often the highest-paying employer for miles around, and they leverage that to the hilt.