Not to be a buzzkill, but my first thought is why buy the epub at all if safety is the main concern? Most online libraries carry it, and you can likely borrow it digitally for free. Libby through your local library is the safest, most legit route—no credit card info floating around, no weird third-party sellers. If you're dead set on owning it, Apple Books and Google Play Books have never given me any trouble; they're straight from the source, so to speak, and the file works across my devices without needing some sketchy converter.
That said, if you're looking for a deal, the 'safely' part gets tricky. I've seen '48 Laws' pop up on sites like Humble Bundle occasionally, packaged with other nonfiction. Those are legit. But random ebook marketplaces? I'd steer clear. The epub format is easy to pirate and repackage, so you might end up with a messed-up file or worse. Honestly, paying the full price on Kobo or Amazon for the peace of mind is worth it. The book's been out forever, so it's not like you're waiting for a sale. My copy's from Kobo, and it's fine—notes sync, formatting's clean.