It looks pretty official to me.
This may change depending on your browser, but with most browsers, you can see that the site has a locked padlock symbol to the left of the URL. This means that any data you send to this site is encrypted, and difficult for third parties to decode. You should always look for this symbol on any site you intend to do a paid transaction on, so this is a good sign. Additionally, clicking on the lock gives you more information about it, which for this site will tell you that it has a certificate showing that it is officially owned by The Pokémon Company International.
I haven't personally purchased anything from the site in the past, but everything about it checks out. If I was interested in buying something from this site, I would be willing to trust it.