It’s legal because they warn you. They have a pop up explaining how it works and that by continuing you’re consenting to be charged at the end of the sale; that’s before you can even view the sale. Then they have text about it on the bottom of the cart page as well as multiple banners. They send you an email the day before the sale closes warning you and I’m fairly sure they send you one at the beginning too. And they still usually cancel it if you catch it before it ships. No disrespect meant to anyone this happens to, but clearly they weren’t paying attention to miss all of the warnings.

I’ve filled up carts in the middle of the night and abandoned them too, but CC information is an extra step in that process.