[member="Alexander Jourgun"]
How do credits work... Well aside from the idea of being a universal currency it is a great means of adding a slightly more immersive part of your roleplay experience.
It can be arbitrarily said that your character has wealth or comes from wealth and thus may not have much to worry about it.
Its all up to how you much you want to involve it with your character along with the circumstances of how your character lives.
For example my character Caius Flavian is a member of a military/government organization and so a lot of things are or can be provided for him such as, weapons, armor, healthcare, shelter, clothing, food, and receives regular pay. However all of those things can just as easily be taken away. So credits play a role in my characters personal life He is member of a company, invests it into different projects that hopefully will have greater returns (he is also near broke and totally will be riding the IOU wave until he gets back to the Empire...)
You are a new bounter hunter or mercenary? Great what did you start with in terms of gear and what motivates your character to get more? Now what do you have to do to acquire these items or things? Once you get the credits do you want to keep track of them? Sure if it helps the immersion or meh I just get the stuff and say "thanks to the last mission I got enough credits to afford these things"
So yeah the market place is definitely a means of providing incentive to "spend" your credits on things, it is however Out of Character oriented more so than In Character. I've made that little snafu a few times but what is great is finding a "vendor" out of character and saying "Hey I want to get some of the gear your company sells for my character" so you set up a roleplay thread where that transaction takes place. Hell you can even write it off as a tertiary thing such as "today I'm going to submit an order for X number of plasteel armor plates cause I like to have extra gear just in case".
As [member="Celty Ikon"] stated you can go about getting gear in others way than the market place as well. Perhaps having performed a mission for another Character they give you"stuff" or maybe you want go forge your own armor and gunsmith your own blaster so you can about it that way as well! Crochet a sweater! (note you ned to buy needle and thread for that one soooo credits may be required"
You could steal a ship rather than buy a ship.
Credits just allow you to acquire things legitmately or illegitmately but are really just another optional tool in aiding your writing.
Hope this helps!
