I had this happen to me today. It actually happens to me all the time, but then I have found that in Ireland this is the norm.
As I am still building my round, I have plenty of gaps in my schedule, and as most of my work is less than 10 minutes from home, for the time being I am going with it and being flexible. When I have a full book, I will probably say that if it is inconvenient to do them today, I will be happy to do them next time I am in the area.
John