IThe selling prices of these businesses are on the order of 20-25x monthly profits, so two years of profits and the business paid for itself.
20-25x monthly earnings is really high. You should only pay closer to 12 months earnings.
What's the catch, and why do websites go for much less price-to-earnings compared to non-online businesses? Because next month Google could change their algorithm and your traffic could be cut in half. Amazon could start selling your product. The previous owner could have been (probably was) lying to you in some way. The dropshipper could disappear. Who's handling the money for you? Paypal will give your money to just about any person that files a claim. Are you sure the website's content isn't violating copyrights? Online security? How are back-ups handled? Is the seller showing you ALL of the books? How much is hosting costing them?
Having run a successful e-commerce site in the past that did over a half a million in revenue per year and that used dropshipping, I can tell you that you will spend WAY more than a few hours a week. Your primary job now is customer service and dealing with disgruntled customers. At least 10% of the products shipped will have problems if you are not handling your own inventory (dropshipping). You will also be constantly finding new suppliers, dealing with payment processor issues and charge-backs, updating content, SEO work, etc. I killed my own e-commerce business a while ago because I make far more per hour in my current career that I actually enjoy.
It's a business. Definitely not all sunshine and rainbows. And any website listing that says "a few hours per week" should send you running away, because they're lying, and if they're lying about that, they're lying about everything else, too.