Many private search engines use the same business model as mainstream search engines to generate revenue.
Advertising: The top few search results are likely to be ads, no matter which type of search engine you use. However, with private search engines, you might find they are more relevant to your search query.
Affiliate links: The search engine may earn a commission if you purchase something after clicking on a link from the search engine results.
Online shopping links: The list of products displayed on the right-hand side of your search results are likely to be from an affiliate partner’s product feed. Again, the search engine will earn a small commission if you purchase something from here.
Some also offer a premium paid version, usually providing an ad-free experience.