Answer:

trading

Answer	Crossword Clue
TRADING	Post activity
TRADING	Market activity
TRADING	Basis of international economy.

TRADING	Buying and selling.
TRADING	Kind of stamp.
TRADING	Kind of stamp
TRADING	Off-season baseball action
TRADING	John Jacob Astor's activity
TRADING	Kind of post or stamp
TRADING	Wall Street activity
TRADING	Activity for folks in the pits?

TRADING	Exchanging.