I just noticed there is a new preview option available on the Kobo website. I can preview a book in a popup window in my browser, I don't need to be logged in or download the preview to a Kobo app or device.
This is from the New Zealand site, it might not be everywhere, so I've added some screenshots of what I see:
This is from the New Zealand site, it might not be everywhere, so I've added some screenshots of what I see: