Very original idea and executed well - you got so much into a week's work!
I enjoyed practising a bit of maths and the concept of taking off a little more on top. Remembering and planning out what rules applied was also fun, it's a good puzzle game!
I wish there was more of a mechanic to haggling/persuading people when they are refusing to pay. I imagine that's where the probability comes in, but because this isn't visualized in any way I don't understand the risk as easily. This may be in part because you want the player to work out the correct amount themselves so you can't show the range of how much the player is over or under I guess, but it means that in some places I feel a little out of control and at the whim of the RNG.
I liked the map travel, only wish something had more clearly indicated where I am at any given point, I lost myself on the map at times.
The graphics were nice, though I think there's a bit too much of a mix of different art styles and the pixel art clashes with the other UI elements. All the assets are great on their own, but I think the overall style could be more cohesive.
Super cool concept and execution overall! Great work!