When you have a vacant rental, you will inevitable have to advertise and fill it. Unless you are extremely lucky, you will not rent to the first person who inquires on your rental — or at least the first person will not likely be qualified to live in it. You want to get the best tenants you can possibly attract to your rental.
Like it or not, you will be at some point showing your property to tenants that do not want to rent from you, or you do not want to rent to.
At some point, you will need to decline a rental applicant. This is one of the main problems landlords have: being unable to decline a tenant.