About a month ago Lego let me take a closer look at the new Harry Potter sets that are due to be released next Wednesday. If seeing those pictures got you nice and excited for the next wave of magical Lego bricks, you'll probably be happy to hear eBay will let you pre-order them right now. Not even the Lego store has that option yet.
All the incoming sets are available to order on eBay's dedicated Lego Harry Potter page, including the minifigure blind bags that I didn't get to see in person. Most of the sets are still full price but you can get 5 per cent off Hogwarts Castle. Other discounts include 8 per cent off when you buy all of them, and six per cent if you buy Hogwarts bundled with either the Whomping Willow (which it combines with) or the Hogwarts Express. The bundles are only available in limited quantities, though.
The downside is that these sets won't be arriving next week. According to the delivery estimates the earliest they'll arrive is the 8th August, and that's only if you pay for shipping. If you want the sets quickly you'd be better off heading to your nearest Lego store and picking them up in person. That said, it's probably no longer than you'd have to wait buying directly from the Lego website, with the added bonus being that there's no minimum spend for free delivery.
So if you want to guarantee your order right now, you can. Otherwise to can try your luck with getting it from someone else after the sets have been properly released. It probably won't be too hard, but Harry Potter is popular enough that these might initially sell out for a bit. Just remember ordering through eBay won't get you any VIP points, nor will you get whatever free gifts Lego has on offer.