What are some useful dataset API functions?

Fellow developers,

I am considering selling data that I've collected through web scraping, and I want to get some feedback on what sort of API functionalities would be most beneficial to expose. And what sort of features would make it most valuable to you as a buyer?

Also, I am curious about how to handle selling data with a subscription. What are some best practices or things to consider when setting up a subscription-based API?

Thanks in advance for your input!