Ah, yes, x9jaan described the best way to get people for bribery - and it shows the principle:
if you have bathhouse people in the game's memory they will still be there after loading your savegame.
Concerning arbitrage unfortunately I can't help very much except in one point.
The principle here is:
You have to set a sell max price which is
lower than your buy max price!
You gain money only by your captains trading talent. Believe me, it works.
The idea behind this principle is to earn money day by day without sea trade.
And the amount of money can become huge while playing longer and longer.
Maybe someone else here on board can help with details, I never used the fascinating arbitrage in my games.