Finding an apartment is very similar to finding a new job. First impressions count.
I have been doing rentals for several years and one of the tools I use to determine whether a prospect applying for an apartment is going to be a good tenant is that I have them confirm the appointment the day of the appointment.
Typically, the appointment is set up a few days in advance. So, I have them contact me the day of the appointment to confirm. If I do not receive the confirmation, then I assume the prospect is not interested in seeing the apartment.
While there are valid reasons to cancel an appointment or to call in the future to reschedule, I lost the phone number or I decided to have lunch with friends, are not good reasons.
Show a landlord or Realtor that you are responsible and considerate of other people's time and energy. This will serve you well in life.