To My Trusted Advisors;
It has now been six months since the founding of Puzzleville around the entrance to the magic-filled Labyrinth of Wonders. As expected, adventurers from around the world have braved the subterranean depths to extract the countless artifacts left behind by the maze's builder, the elven mage Parasaxor. The city's population and wealth have exploded these past months.
Unfortunately, so too has the number of magic items increased dramatically. There have been complaints from the adventurers that a majority of the items they find are insufficient to their needs or inferior to their existing equipment. As a result, they often pawn the goods to the merchants of Puzzleville.
Four times now, merchants benefiting from this influx of powerful magic have become delirious with power, using the wonders of the Labyrinth against their fellow citizens and to exact retribution for past slights or force payment of old debts. This is, of course, upsetting to hear. However, it has caused some adventurers to take their business to merchants in other locales, where the influx is starting to have a similar effect.
The king has been made aware of this growing problem and has charged me with presenting a solution within the next few days. As you are well aware, His Majesty has concerns regarding the use of magic, especially after the pie incident at the recent Thanks Festival. As such, I am asking each of you to formulate a mundane solution to the problem I have outlined above.
Please have your plan on my desk as soon as possible. The solution that imposes the least impact on the merchants and the Merchant Guild while safeguarding the royal coffers and all levels of the economy will be implemented.
First Treasurer to the King
P.S.: Remember that the roads are unsafe in our Medieval world. Stay safe while traveling for this year's hibernal solstice celebrations.
Adventurers are treated in the region as a necessity. They help keep the growing monster population in check and deal with mages that become crazed and/or delusional, some of whom even build elaborate subterranean vaults filled with magical artifacts. Adventurers typically don't receive support from the government; they make their livelihood purely through adventuring, though they may receive a commission for undertaking certain tasks on behalf of the government or an individual. As a result, the common folk are happy, but cautious, about the average adventurer.
This question is only concerned with merchants, not the issues of thieves that necessarily arise parallel to the merchant issue. Also, note that this is not an issue with all merchants, but only the ones that are particularly aggrieved/vengeful/etc. Finally, while mages are available, this question is specifically focused on defining a non-magical solution.