I believe I have read that any race recognized by IAAF must be measured by an IAAF "A" or "B" measurer. I see their point, but if a Grade "A" measurer participates in the majority of the measurement, has a flat, then observes the other rider for the remainder of the ride, I am with both of you - the measurement should be accepted.
If I have to travel, I always have them book a room for at least two nights, so if there is an issue on the first day of measurement, I have one more morning to measure. It takes time from my real job, but I sure don't want to travel, then not have time to complete the job on that trip.
While our job is not really difficult from a physical perspective (some courses are more difficult than most), we do have technical issues that take time and consideration. Always book more time than you think you need. I can usually come home early, with no penalty to the race for the cancelled second night.