How to reference data someone told me in person? As a part of one of the graduate course I am taking, I need to develop a business plan for a coffee shop startup. I have chosen a office building as the location of the shop.

I want to provide some numeric data about the building. I had a chat with the financial investor of the building and he gave me some numbers giving clues on how profitable the coffee shop will be.

As this data is not from a credible resource I am afraid that the marker may assume I have made it up.

Do you think can I still make use of this data without treated as a plagiarist (or perhaps data fabrication)?
The conventional way to attribute such information in your references is to cite your source as "So-and-so" (i.e. the person's name) -- "personal communication".   Of course you should get the person's permission to reference them, ideally in an email or some other written format, to be sure that there will be no miscommunication about them having given permission for you to reference them and the numbers they told you. HTH.