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There are some commercial vegan diets available which have synthetically made nutrients to replace those found only in animal based ingredients.
The discussion is about commercial vegan cat food, which had the nutrients cats need, just sourced without killing other animals. The science on these diets is still relatively new, but early studies are looking pretty good.
Companies pay for free returns by increasing their prices by about 10% to cover the cost of reverse logistics. Most of the items returned in online shopping end up in landfill.
Most of what it worthwhile to buy from Amazon can be found in a physical store or from the manufacturers website. Do a bit of research beforehand and it’s very easy to be confident that you’re not going to need to return what you buy.