Being adept at a particular trade.

Manufacturing Killers Utilizing Lethal Tradecraft Requiring Assassinations

Yes. All world agencies have in-house schools.

However, if you are not a member of an "agency," for whatever reason, you may acquire spy skills or tradecraft by other means. One such example can be found at www.meetup.com/the-seattle-tradecraft-group

They really didnt have technology. Damian Fettes (Elven Philosopher)

Randall E. Puig has written:

'Intelligence tradecraft primer and media exposure' -- subject(s): Intelligence service, Methodology, Mass media and publicity