Harry Potter had a first print run of 500 hardbacks, Zazou. Plus, I'm pretty sure I read that it was 1500 hardbacks sold in Britain - it's also available in paperback & kindle & there's a US edition as well. Regardless, 1500 in the first 3 months with all-over favorable reviews for an (alleged) first timer ain't that bad.

There's not a lot of money in writing for most authors. Unless you're JK Rowling.

PS - I think the publication of the Casual Vacancy was an interesting exercise. Agree it was a forgettable novel. It may not even have flown for anyone else without the profile. But even despite the lackluster reviews, there was a lot of hype and it sold reasonably. but reading it was seeing an otherwise seasoned author making a common rookie mistake. I'm guessing JK probably learnt some lessons that might have bypassed her earlier in her publishing career because of the unusual success she enjoyed.