Suggestion: Enemy NPC's can drop money when defeated - working remains significantly more efficient for earning money - amount earned depends on difficulty and has an RNG element (slime's in the starting lab area ? 0-0, Bandits in the starting town ? 0-5, Mansion with the tough staff ? 0-50, etc - pretty much the harder the fight the greater the possible cash reward but can always be zero). Pretty much a bonus reward and gives an alternate solution to getting into new ark (lots of grinding required but possible) and/or another way to get past the thug without becoming a dancer.
I'm sure there could a valid reason for the money earned seeing as the idea the PC is robbing NPC's after defeating is unacceptable. The only thing that comes to mind at the moment is perhaps the NPC's are paying the PC for help improving, kind of like a physical trainer - PC gains points even if they lose a combat fight so something like that but the generic NPC's generally don't actually get stronger. and the variable amount could be attributed to how much the NPC feels the training session was worth - did not feel any improvement ? 0 credits, Felt a significant improvement ? Maximum credits.