Fucking with market flow is a criminal act, while that's a creative way to punish it it's not leaving the punishing up to the people affected, it's letting the game decide.
Having a seal that lets you stamp everything (as has been suggested and received rather well, even by the devs iirc) would be neat, if it also stamped coins it'd solve this problem too.
It'd actually be VERY neat if said stamp could stamp IGNs a certain way, like let's say if you choose "Stamp Hearthling's Name" it stamps your name on it and it's a nice dark blue (A color not reproducible otherwise), same should work with "Stamp Village Name" so that if you wish to have a system of anything (not just coins) work based on your Hearthling's name or your Village name, you can.
The 'stamp' or what have you should be able to be rubbed/washed off too.