To add vendor details go to Setup → User Fields.
Click User Fields and then click Brokerage User Fields.
Select Vendor Details next.
Within the Vendor Details, you may create detail fields for your vendors. This could be information that you want your agents to fill in. To add more detail questions, click the green "Add Item" button on the bottom right. To make sure a detail appears in the vendor tab, the active boxes must be checked for it to appear. Select the option Include in transaction summary PDF if you want it to appear in the transaction summary PDF report.