There's a difference too between allowing self-hosted JS and 3rd party JS. As a no-script user, if a site does not work with JS blocked, I will allow self-hosted JS while still blocking 3rd party. If it still doesn't work, then I consider if the site is something I'm really interested in or not. If not, tab closes. If I am, then I'll look to see if there's 3rd party stuff I trust.
In your example, allowing Amazon's JS allows the site to work at least as far as AWS Console behaves. I don't really use eBay, so I can't speak to what JS is required.