Costco doesn't install anything. They sub contract with local fabricators, just like every Home Depot and Lowes. And the quality all depends on that local fabricator choice. Which is far more iffy than you think.

Lowest bidder?

"And the quality all depends on that local fabricator choice. Which is far more iffy than you think."

You'll find that big box and Costco fabricators/installers are overwhelmingly large, established, and reputable. The contracts to get the big box work are very valuable and out of the reach of smaller players.

Years ago, Lowe's wanted to award all of its countertop work to a single fabricator in the state of Michigan. My former employer, a larger player, still wasn't big enough to give them their wish, so he formed a new corporation with two other fabricators and they split the state into thirds.

Thank you!