So, I was killing mobs on singleplayer, and I found that they don't drop credits. Is that supposed to happen?

i used a couple mods to recreate some of the server trading food for credits and it seemed to work so maybe if you wanted to create shops in singleplayer you could use the custom villagers mod and vanilla inspired teleported and a few others like that

Well 99% of my DM playtime is on DMU anyway :)