[glofish]

the question here is of course, how should one classify a manufacturing defect that affects a tiny percentage of the product?

Is that a merchantability issue? Is it realistic for a merchant to test every single product so extensively to uncover a defect of such a rare occurance?

One of the greatest ingredients of justice in the USA is that laws can be interpreted by a jury. I would most certainly vote against applying this "merchantability" blindly - without more context and more proof of negligence beyond simply stocking a product. If one in a hundred thousand catches on fire and the product is pulled makes for a very different story than if every other ignites yet they keep selling it.

[TheCoelacanth]

They don't need to individually test every single product, they just need to make sure that they can turn around and sue the supplier if the product turns out too be defective. If they have no means to hold their suppliers accountable for the quality of the product, then they should be testing every single product.