How can I effectively check that Polish workers are competent?  I have certificates in Polish for Banksman/Slinger which is 4 years old.  The certificates are valid for 5 years in Poland! Any advice on what I can do to ensure competency prior to them starting work on site.

Get a competent banksman/slinger to test them noting this is the perocess that has been used sucessfully forever as only a competent person can evaluate if somebody else is competent

Courses, even good ones; very few as they are, are just courses they do not make somebody competent