Why would it be illegal? Unless the product is proven to be defective or unsafe, I can't see how you could force a company to accept a refund when someone changes their mind. Companies only do this when they think it is good for their reputation. They aren't going to care that a price gouger gets stuck with thousands in losses.

In Australia we have strong consumer protection, but not for changing your mind. It's a courtesy most retailers offer but you clearly don't deserve it when you realise you don't need 2000 tools of tp.

I think where supermarkets give refunds at all for non-defective products, it’s generally discretionary.