[ARCHIVE ANSWER]
I would say it is 50/50. The dog seems to develop the personality of the handler.
Proactive and high energy handlers like me would tend to have a dog over-alert.
The more calm handlers that are reactive tend to have dogs under-alert.
An under-alerter does not alert any person further because it did not alert. An
over-alerter causes such mistrust between the handler and dog that the handler
often pulls his dog away from alerts and does not search. I've done this very thing:
I stopped a Mexican male traveling with a white female. The car was traveling
West on the Interstate, so I was looking for money. I tried to get my dog to search
the car, but he kept alerting on the red ice chest. The cooler was full of ice, water,
and general cooler items. After finding nothing, I let them go. One week later, the
same couple in the same car was stopped by border patrol. The K-9 alerted on the
cooler. About $80,000 cash was found secreted between the coolers liners. The
insulation had been replaced with money. So I missed a large money load because
I did not believe my "over-alerting dog."