Book Sponsors

In a word, yes. That's basically self-publishing. I've never heard of a reputable non-self-publisher doing that.

How reputable is the publisher? It sounds very self-publishing-scammy to me.

Have you checked Bewares, Recommendations & Background Checks yet?

But, yeah. ANY publisher who requires someone to purchase a number of books, whether it's the author or a 'sponsor', is a vanity press, plain and simple. Commercial and trade publisher sell books to shops and readers, not to authors and 'sponsors'.

I agree. Nonfiction houses often ask if the author if s/he had such platforms, because that makes the book more appealing--you can justify a 3,000-copy print run if you know that the author's floral society will probably want to buy 500 copies on top of the ones your distributor gets into the bookstores. So you can expect a question about any special connections you might have; that's totally normal.

But it's just asking about platforms and potential sales, and that's a huge difference. I'd cross-check this publisher on the aforementioned Bewares forum, and on Preditors and Editors, if I were you. That request is not quite on.