Yup, Costco is a great source. I emailed them and asked about the fake oils. They said they do random testing of every shipment.

First, I avoid most of the m vegetable oils in general. Not just for cooking. The only exceptions is olive and coconut. Most oils are high in omega 6 fatty acids. This skews the ratio of omega 3 to omega 6 that our body desires. But cooking or heating the oils makes them even worse. It destroys good properties, oils become rancid / oxidizes during heating.

I just don’t see the reason to even use veg oils. Food tastes so much better cooked in butter or ghee, or bacon fat, or beef tallow.