When we get a call from a BUYER I never spoke to before, we explain that we need to meet in the ofice - sellers expect that we have met with the BUYERS and that they are pre-approved for a mortgage - and sellers expect a 24 hour notice before showing (preferrably).
Now, some BUYERS will insist on meeting at the house. We will give them the benefit of the doubt - the first time only. We will also call them BEFORE we go out to remind them of our appointment. If we get a voice mail or answering machine, we ask that they call us back to reconfirm the appointment.
If they're a no-show. We will call. If we get no answer and if they're a no show after 30 minutes, we will leave. If they happen to call back, we will tell them that we are not able to work with them. Period. End of discussion.
We've had it happen where they were a no show. If they're a no-show and if they didn't have the courtesy to call us, they do not get a second change - ever!