The Sanctity of the Markets Curse (Or the Sanctity of the Markets Blessing) was a rare curse that could be found in select cities around Quelmar, most notable Al'Adeaf, which was placed by the god of trade Waukeen/Denari.
About
The curse was originally devised as a boon by clerics of Waukeen, but it became known over the years as a curse more than a blessing. The curse caused Corruption in spellcasters and on magic in general when cast within the city's limits.
The corruption manifested in a number of ways. These were categorized as "Internal Corruption" and "External Corruption"
Internal Corruption
External Corruption
Behind the Screen
Corruption comes from Swords of the Serpentine, and was brought into Quelmar to explain why in some places (especially investigation heavy places like Al'Adeaf) magicians can't just show up (Such as The Lich Omoi) and magically devine all of the answers and prophecies they would need to solve a case from the comfort of their living rooms.