finding high-quality mobi or PDF versions of bestsellers can be a real treasure hunt. The best legal route is to check platforms like Amazon Kindle Store, where many bestsellers offer mobi formats directly. Project Gutenberg is a goldmine for classic bestsellers that are in the public domain—everything from 'Pride and Prejudice' to 'Sherlock Holmes' is available there in multiple formats, including mobi and PDF.
For newer titles, I often rely on Humble Bundle's book bundles, which sometimes include bestsellers in DRM-free formats. Authors like Brandon Sanderson and Neil Gaiman have had their works featured there. If you're part of any ebook-focused Discord communities, members often share legit free promotions or temporary deals from publishers. Just remember, pirated sites might pop up in search results, but they’re risky—sketchy downloads, malware, and poor formatting aren’t worth it when so many legal options exist.