All I would propose is GIVE, GET, BUY, and SELL. GIVE and GET are as
you describe. I've said why I think it's reasonable to allow, say, the
captain of a ship to buy and sell goods in the city. If you like, the
merchants come to the docks to do business with him. Since BUY and SELL
effectively involve invisible middlemen, it's easy to imagine admitting
those middlemen to your ship without admitting an unknown stranger.
I would not allow EXPLORE, COLLECT (and its aliases), PILLAGE, ATTACK,
or similar commands from within a sublocation. I also think these
introduce some additional complexities which are best avoided.