To deal with such situations, Facebook has added a feature that allows users to completely ignore messages from a particular person without letting them know or blocking them.
Latest version of Messenger app
Working internet connection
Steps to ignore messages on Facebook
Open Messenger website and login using Facebook credentials
Head to the chat window of the person and click on ‘i’ button from the top right corner
Now, click on Privacy and Support option and then click on Ignore messages option
Choose Ignore Messages option in the confirmation popup.
On mobile app
Open Messenger and head to the chat window
Tap on ‘i’ button, scroll-down and choose Ignore Messages option
Confirm to ignore all the messages from that particular person.