METHOD TO GET RICH:
Transmute base metals to gold, or conjure gold out of thin air.
WHY IT WON'T WORK:
As with the other conjurations/transmutations everything has a duration. While it's not impossible for someone to conjure up gold or transmute another metal into gold, sooner or later that gold will return to the base metal or vanish into thin air.
Another reason - and it's pure speculation - conjured/transmuted gold isn't as effective in magical applications as the real thing.
STORY IDEA: NB This is more of a background idea than a specific storyline. Someone has already conjured up a huge amount of gold. A staggering amount in fact, possibly conjured to pay for Napoleon's empire building. Unfortunately the wizard in question died just after Waterloo. This in and of itself, is not the problem. The problem lies in what happened to the conjured gold. The conjuration was very well done, designed to last many mortal lifetimes. And over the past three centuries the gold has been dispersed across the globe. While some of it was crafted into plates, chalices, jewelery etc, much of it was in the form of coins and bullion. Coins and bullion that has since been passed around, melted down and used for a variety of other purposes, including electronic componants in aircraft, missiles and satellites. And the duration has just come to an end. What starts off as a series of mysterious electronic failures in aircraft, escalates as several key satellites begin to fail. Museums and private collectors report thefts of valuable gold artifacts from the Napoleonic wars.
For a more specific storyline, perhaps the wizard in question linked his conjured gold to an item (kind of a sympathetic link for his entire gold conjuration). Some nasty enemy warlocks have gotten their hands on the item and have ascertained that they can make key sections of one country's defence network stop working if they can dispel the magic on the key item.
The item in question was in the hands of the apprentice to the original wizard (himself now a wizard of some repute) and he's been regularly maintianing the spell because he knows what the gold has been used for. Unfortunately he's never been able to duplicate his former master's expertise and his own enchantments can only maintain it for a few years at a time. The PCs are asked to investigate his murder (or maybe he's a friend to them and they decide on their own to find his killers), and discover the item to have been stolen. Now they have to work out who has it and why.
If you use the idea of the gold being transmuted rather than conjured from nothing, and don't want to explore the possibilities of the gold having been used in electronics, then you have the option of the PCs being brought in to investigate several high profile gold artifact thefts, where the artifact has been replaced by an exact duplicate in lead. In this scenario you can ignore the apprentice and the key item, but you can explore what happens when a large amount gold in one of the world's bullion stores is suddenly found to have been replaced by lead.
