I search, see the results, and then click on a result to view the applicable contents of a particular book. In the contents that get displayed, the search term I had entered is highlighted.
a) sometimes the snippet returned doesn't even contain the search term
b) you'll only get the snippets for the first three results, and that's that.
There might be even cases where the book is indexed, but the publisher has disabled even snippets, but I'm not sure about that. But a very limited snippets-only search instead of a full preview is certainly a thing.
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I mean, the domain resolves, but that doesn't mean the product exists. You can run searches, but you're not allowed to see the results.