Requirements collecting
An answer to the third question: "How to build trust to make use of data science for the business operations?"

It heavily depends on the type and structure of data that you want to get access and the application that you want to provide. 

For example, if data owner has a concern about the privacy of its users, and you just want to execute some statistical queries over their data, you should design and propose a privacy-preserving method for accessing to their data. There are some techniques like Differential Privacy (or Randomized Response) which provide a well-defined privacy guarantee for data owner.