It is one of those delicate social moments: you are dealing with somebody who needs potential access to information that is personal, confidential, or privileged. They might be a contractor, cleaner, or repair person who might overlook or overhear something, a temp, a new staff member, your IT expert, etc. Assure, in every possible instance, that they are bound by a confidentiality agreement, either with you directly or an intermediary (building management, the IT company, temp agency, etc).
You should reduce risks to a minimum within your physical space – no agreement is a substitute for good confidentiality practices.
Resources for Confidentiality Agreements
Law Society of Ontario, “Confidentiality Agreement” (April 2012). lso.ca.
This agreement is a bit more extensive, which works for staff. You can use your professional skill and judgment to adapt any of these. There are other examples out there.