While that may not help with the arguments over the correct dosage, it at least means you can trust the ingredients and dosage on the label isn't a lie. A random mail order supplement or bulk powder seller on Amazon...not so much.
Which is some entity who cares, or who would approve plutonium as a school lunch if the factory paid enough?
https://www.usp.org/about/usp-convention
I will actually point out an amusing note about Walmart's pharmacy services - you find them in weird places. https://www.delta.com/us/en/careers/corporate-careers
Towards the bottom of the page at Delta's careers page you'll note that Delta's headquarters in Atlanta has a Walmart Pharmacy in it. Delta is essentially signalling to its constantly moving employees that you're more likely to find a Walmart near an airport than a CVS or a Walgreens (especially in super-rural America) and that pharmacy is a constant stream of pilots and flight attendants grabbing refills on their way through.