Do Amazon ads actually work for a debut author with no reviews yet?

With zero reviews, ads will mostly light money on fire — not because the ads are bad but because your product page can't convert the clicks you're paying for. An ad's job is to get someone to the page; the cover, blurb and reviews do the actual selling. Send paid traffic to a page with no reviews and you pay for clicks that bounce. So the order matters: get the page right first. Aim for a handful of honest reviews (ARC readers, your newsletter, friends who'll actually read it), tighten the blurb, make sure the cover reads well at thumbnail size. Once you're converting organic and gifted traffic reasonably, then start ads small — a few dollars a day on tightly targeted product/category ads — and treat the first month as buying data, not sales. Scale only the keywords that are actually profitable.