If a list agent runs a Reverse Prospecting search for their listing and sees that one of your Contacts has a saved search that matches their listing, they may reach out to you to see if it is a good match. Please rest assured that your Contacts' information is always confidential- the only thing any other Matrix users will ever see about them is a randomly assigned reference number.
The list agent can use this reference number to identify which of your Contacts has a search that matches their listing.
You can find your Contacts' reference number by going to My Matrix> Contacts. The Ref# column is on the far right: