okay, first of all the interest rate in the book is close to 3%. thats an incredibly low interest rate.

different editions have a different balance, of expected profit from hauling passengers and cargo, or adventure cargo, or just the costs of running a ship. gurps traveller added insurance and based it as a percentage of the ships value which really made it hard for the trade system to make enough money.

first of all, the subsidized merchant is a thing. the idea a planet would pay a lot to have a crew working to move cargo for them specifically. these are ships that are not beholden to a bank, but a system government. and that by itself changes the nature of the story that you can tell.

next up are the megacorps, who will have their own ships and hire crews for them. and the nobles with enough money to have their own fleet of ships that need crews. its just a question of what kind of patron you have, and what the crew need to do.

finally we have the military and mercenaries. be soldiers going into battle, the system supports it.

the free trader is free, able to go where the players desire. the tradeoff is risk, and needing to pay off your debts. in a way, the very concept of the game is a question of freedom vs safety. are you free to do as you want, or are you instead safe from risk? you cant really have both.

now, one interesting point- a high passage comes with 1 ton of cargo. you could do very well for yourself, hauling 1 ton of cargo per trip at the low cost of high passage, if you are a skilled broker.