There’s a good reason why ClickBank is still a strong contender, however it does tend to focus more on digital products which may be of questionable quality. Yes, the review process is more professional these days, but it’s still primarily focused on selling digital products, especially “how to make money” courses and the like. That being said, there are some genuinely high-quality products on offer, and few affiliate programs are bigger than ClickBank, especially in selling (primarily digital) books.
Hunt for under-priced used books that you can sell online. Download an app that reads ISBN numbers so you can scan the barcodes on books. This will pull up the book’s current price on Amazon so you can see if it’s worth trying to resell it. Then, visit used book stores, thrift stores, and garage sales to look for high value books. Post the books for sale online using sites like Amazon or Ebay.