In reply to The Ice Doctor:
Theres too many variables in your question to answer it usefully but...
If a person had done a training course, with no assessment element then it tells you very little about them. Just because they have been taught something does not mean they can do it well. So no.
If a person has been through a competency assessment and passed, then there is a benchmark on which you can make an informed opinion.
In the context of expedition leading, I think experience is key. A person should hold a relevant qualification, and have a substantial logbook of experience. Any expedition leader worth their salt will happily share their experience with you.
Ryan