John4

Thank you for your response

Thank you for your response, that fundamentally aligns with what makes sense

Thank you

Welcome John.
I’ve never been in a Costco, we don’t have one in my town yet.
A guy I watch on utube called Old Guy Carnivore gets all his meats at Costco and Sams. They seem to have just about any variety of meat you want. Old Guy buys mostly grass fed beef and Wagyu from them.


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Do check all labels, we have had steak from Walmart that was in salt solution 🤢

The Burger King experience is interesting. I haven't had any Burger King since being on my carnivore diet. They claim 100% USDA beef, although I am sure it's "Standard" grade. But in any event, it should be pretty benign, and therefore edible. I know they had some controversies regarding their meat years and years ago.
But YES, the Costco beef should be good stuff. I get almost all my meat from Sam's Club, and I believe the fresh meat there is either Prime or Choice (Prime is top tier and will cost more). I usually buy the Choice cuts to save money. 
They also have prepackaged Wagyu as well as Grass Fed, and I get both of these as well. 
I don't think you will have a problem with Costco meats, at least in the fresh meat sections. I might be more leary of buying a frozen package of burgers, precooked or not, as those would most likely be Select or Standard grade - not that there's anything wrong with that. In the end, meat is meat. The grading has to do with how much marbling is present along with the age of the cow at the time of processing.