Once you remove all of their scheduled appointments, ZenMaid will tag them as "former" clients. 

If you want to inactivate the client listed, you'll have to inactivate all their active and scheduled appointments.

Once you do that, they would be labeled as a Former Customer.

From there, you can use the Actions Button (Contact>Actions) and delete the contact if you wish. This is not recommended if the customer ever had an appointment that created revenue in the account. Deleting removes all information tied to the customer such as invoices, appointments on payroll, & revenue. Deleting cannot be undone & is final.