Don't assume that people will not just create 100 accounts to be "king".
The problem for them being if it's a democracy they can only be "king" for, say, a month or so. Then they can not be "king" again for say 6 months or something like that. If someone wanted to create 100 accounts for a paid MMO to get elected then it's a win for us developers as it's money in our pockets . You also only give the "king" limited rights to minimize the damage they can do in a short amount of time. There will be people who want to be "king" because they can do more stuff than normal players. Even if the more stuff isn't all that intense it's still something more and there will always be someone who wants to be special.
I would just have player hired NPC merchants. They could charge money % of the value players placed on the goods they are selling or a baseline merchant fee. If you don't pay the fee, poof they go, taking your goods as their fee. If you want your goods back, you can go to the NPC merchant hiring area and pay the owed fee for the return of your goods. There would be an interest rate so it couldn't be used as infinite storage.
You can do this with people as well with contracts. No need for NPC's. I can give contracts out that says 1 contract can chop down 5 trees on my land. I get the wood and the person doing the chopping gets x currency per wood qty. These contracts can be in a classified area on some newspaper and anyone can accept. The money is taken out and set aside when I make up the contract to ensure I have the funds. When the player accepts they are given permission to chop on my land 5 trees and all wood gained doesn't go to them but goes to me. No need for NPC's and now we have an employee/employer situation happening. If someone likes your work and you are reliable they can make specific contracts for individuals.
Interestingly enough this creates a need for a newspaper building, which requires paper from a papermill which requires wood to be turned into paper. To make it so you have towns you can have each newspaper building have a certain radius where people can purchase that paper to see what that town has for jobs, goods, anything.