If you don't want to receive any more inbound texts from a certain number, you have the ability to block their inbound messages going forward.
To block a number in Clientbook, first navigate to the Inbox tab of your dashboard.
Once at the inbox, find the thread of the customer you are wanting to block in the Store Inbox tab.
Once you see the customer's message thread, click on the three dots at the top right corner of the page.
Once in the dropdown, select Block Number.
You will no longer receive messages from this number in Clientbook.