TL;DR: Don't get scammed by the "Book of Providence Eye" (the common bootleg, as I call it). Real copies have a rough paper texture on the jacket, a Bill that looks and feels different from the actual hardcover, and specific colour-coded fabric headbands on the spine (Red/White, Yellow/White, or Green/White). If you're outside the US, themysteryshack.com is the most reliable way to get a genuine B&N Exclusive that actually comes with the Get Out Of Death Free Card, even though it can be expensive, and to copy and paste to other sites to spread the info, please credit me for it please.
Here's the actual thingy (if you want to read it):
If you live outside the US and are far away from the border, your best bet is to go to https://themysteryshack.com/collections/the-book-of-bill.
Is it expensive? Yes. Is it worth it? YES! ABSOLUTELY.
The person who made the site (Jason Kondrake) has a direct line to Hirsch and worked with him for years, so you're a lot more likely to get a genuine copy of either version (Standard or B&N Exclusive). They even stock the LCE! Plus, because they move so much stock, you’re guaranteed to get the latest printing to date, which means all the early typos (like "tcrossovers") are fixed and the books are up-to-date.
I should also say how long the delivery takes depends on where you live. Delivery to the UK usually takes around a week or two. I got my B&NEE from here, and it feels NOTHING like the bootleg I got from other sources (my mother's friend, which I got as a gift. Don't ask. And the book I now call the Book of Providence Eye). My real copy has the proper depth and the jacket feels and looks similar to the standard copy --- the fake is just a flat, slightly oversized mess (yes, it's actually slightly bigger in all directions of our puny 3D perspective) with the B&NEE sticker being part of the cover, and on official copies, the Bill on the jacket looks and feels different from the Bill on the actual hardcover. On the fake, it's just a flat, shiny print. (FYI: some bootlegs like mine do have the 16 extra pages, unlike most common Providence Eyes, but they still look like low-res trash whose only place of belonging is the molten core of an imploding neutron star, so don't get fooled!)
I also want to say that my B&NEE from the Shack also came with that one Get Out Of Death Free Card from the tie-in website (thisisnotawebsitedotcom.com)! Now THAT'S something you'd (probably) never find in a bootleg! (There could be other printable things from there you could get, but I have no idea, as I only own the one.)
I should also say you should get a standard copy first if you don't want to pay a lot of money, for reference, unless you're not a collector. Remember, the outside of the jacket should have that rough paper texture where there is no shiny text or the shiny Bill, which are on the front.
So, Gravity Falls fans, don't risk it on random sites. Go to the Mystery Shack and get the real deal of the darn book!
I've attached some images of the real v. fake comparison, which are at the bottom of the post. And, if anyone's interested, I also have an image of my whole collection (with my hand to prove I own it and it's not edited, and, FYI, I peeled off the sticker of the real B&NEE, in case you're suspicious due to it not being there). I've grouped my official collection together so you can see the difference in quality.
Whether it's the Standard, the B&N Exclusive (which I got from the Shack, as I said), or the LCE, the real books have a presence that the bootleg below them just can't match. You can see the way the official jackets and the LCE slipcase actually fit the books properly, unlike the slightly oversized fake.
Also, If you know anyone who might find this very helpful, you can share! And by the way, the website temporarily closes every now and then, so remember, it's better to wait than to fall for the bait! Another thing to look for are the spine headbands—those little fabric bits at the top and bottom of the spine. On real copies, they are colour-coded (Red/White for Standard, Yellow/White for B&NEE, and Green/White for LCE), whereas fakes usually have messy glue and incorrect colours or nothing at all!
(Note: If you're that type of person who deliberately buys fakes, no one's stopping you, but if you're buying it as a gift, you would have a lot of explaining to do once they find out it's a completely inaccurate fake, especially if it doesn't have the extra 16 pages. Sorry, but it's not my fault! And, honestly, you kinda deserve it.)
(Note 2: I have created this guide to help the community avoid obvious fakes. You are welcome to copy and paste this information to other sites (Reddit, Discord, etc.), but you must credit me (pretty please?) and include a link back to this original Fandom post. If you don't, you know the moderators WILL find this, right? ANYWAY, let’s keep the community safe from scammers!)