@rephikul I disagree, since Michio is a cheat he could make 2000 nar after killing 200 of those monster trees during 10 hours, but a normal person on an early stage it will kill fewer includes trips going in and back because of limited storage (around 3 item per box so they carry more in a sandbag or something), on the other hand a party it would kill more but the reward will be split, that aside normal people need to do maintenance to their weapons and armor as well as replacing them after some time including living expenses.
So let's say a "normal person" will kill in 10 hours could kill 20 to 50 monster trees, will give them 20~50 branches which equal to 200~500 nar daily in a year; since it seems taxes are yearly; it will be 73000~182000 nar, that will make to look a very heavy tax on it. since a day in the inn where michio say (a single room) cost 240 nar with dinner, in a year that is 87600 nar, and that's a lot if you still considering that it needs other daily necessities as well as weapon and armor renew or repair.
Certainly, I guess no one will stay in the same floor (like killing slimes for 300 years) and not move on, but still the money earned won't be that much unless you get a treasure box or special items so 100000 nar for one free citizen is a burden, a family of 2 adults and 2 children also as free citizen it will be much worse; so it wouldn't be a problem to sell a relative with no parents at all.
Now if you think about it, a Slave become a commodities so similar to a car or even a property they have a form of taxes or yearly fee as such being a commodity and not a person or citizen it will definitely have lower taxation. So tax on free citizen are quite heavy, since it seems fixed instead it definitely could be around 50% for a normal person and a lower taxation for a slave it definitely be a help for a normal person.
@OiGimmeMoreManga I also want to enjoy such fluffiness.
Edit: sorry for long post!