Courier has a set income since it usually gets a salary and also gets orders from NPC shops, meaning you can play this anytime without really needing other people. Though it does earn quite a bit more when people actually order stuff.
Next up would be EMS, you get a salary + paid per person revived or body removed, though this ofcourse needs other people to die, so will need other people doing stuff.
If you want to look into the jobs of the server, you can go to this link and see what they all do:
https://help.perpheads.com/category/employment
If you dont want any of these jobs for reasons, fishing would be your best legal bet:
https://help.perpheads.com/page/fishing-guide