Genies? wait what?
When the economy of your world can be messed up with wishes
Ok, gave the plot away with the header, but hey, lets just make it clear and simple:
TL;DR; A Wish, can ruin your game.
I Wish for a room filled with gold coins. for arguments sake, its 10,000 coins.
So, now, the Kingdom that used to have 10,000 gold coins in circulation, has 20,000.
The King used to be the richest with approx. 5,000 in storage, but he's not a stupid king, or at least the people in his city are not, so they mine gold, silver, copper, tin, and maybe some rarer platinum, zircon, etc, at an approximate rate that keeps the currency values around a 10:1 ratio,
except now, the gold in total has just flooded the market.
Are the players going to not spend it? um, no.. So there will be some very large purchases, which will put handfuls of the currency into the hands of a myriad of merchants. they in turn will buy more goods to replenish stock, but also some of their own purchases of personal reasons, and the trickle down happens, as it would / should in a medieval society.
But it also means people are less likely to haggle, why bother wasting time over a 5% price difference, you can afford it, so you pay more, the shop keep gets used to this and doesn't need to sell his goods at a discount to feed his family, so his prices stay high, and his other customers seek cheaper goods elsewhere, or must raise their own prices to compensate for the rise of costs.
If you follow it along, ALL prices will, over the course of a few weeks and months, go up. people are greedy. Without some kind of agent to sweep in and force prices to stabilize, they'll always go up.
In comes the wizard. He casts a spell, and determines the price that a good should be, "mirror mirror on the wall, what was the price of fish last week?"
With some threats, or a charm spell, the prices are forced back to normal for this elite class, and people will come to grips with the ability of magi, thaumists and priests to divine more realistic prices. The Magi know.. if this gets out of hand, spell ingredients will go up in price, and master magi will be forced out into the forests to procure the weeds and flowers they need to create their potions and spells. Magi don't usually sell their goods to lowly folk. they sell once-off items, to the big fish.
Mid to low level adventurers buy healing potions, and sure that's come a little mainstream as a result, but all other magic rings, swords, gems, scrolls, these things are all once-off bespoke items and the magi only sells one every so often, usually for a years salary. So he's not used to having to deal with day to day price increases, no.. he comes to the little shop that has a boy that goes off into the forest once a year and pick the elderflower from the tall oak, that blooms only on 2nd winters solstice, and he pays 100 pewter for it, no more, no less. and if the boy didn't make it.. the magi will weight the costs of a teleport spell to go get it himself this year..
No, no no.. If a Priest was to enter the markets and found out he needed to pay double for all the candles and saffron and gold leaf and statues and marble, he might start flipping tables, and calling his god to come down and smite these greedy heathens.
We, poor saps in the modern world can only grumble at the price of milk going up every year, We look at the real price increases on our expenditure and hope we can ask for an equal pay increase to match it.. just so we can 'stay still', but if we could summon a demon or a god or just the force of the universe to stop it in its tracks, I'm sure we would.
So, this gold.. since its got less ability to create inflation of prices.. the opposite happens.. its own worth changes. After the few months of prices going up and back down.. the gold is still so much more commonly about. more people have it, so people start to say, 'hey, I know I should give you 10:1 ratio on your gold, but I don't have as many pewter, so how about I give you 9:1, and since I kind-of don't 'need' as much, as I got paid in more gold last week, I don't need more, then you make the choice, 9:1 for my goods, or go find a money lender, who'll exchange money, and take his cut.. greedy bastards.
That's right, you probably don't know. people didn't carry around large sums of cash in markets. they'd get robbed. the 'till' we have today would be emptied by thieves in moments. No, they had mobile bankers.. or moneylenders, who'd roam about with a couple of thugs for protection. thugs cost money, so the lender would charge a fee on exchanges and loans. If the going rate was 10:1, you might get 9.5:1 from the lender, or vice versa 1:10.5 if you wanted a lighter purse. You could call him over when a customer had currency you couldn't deal with,
Now, lenders are more aware of the current flow of cash, so if they know there is a bucket or barrel of gold flowing into the purses, they're not going to stick with a 9:1 ratio. no, no.. they'll want to be ahead of the game, and have some street urchin go find out how much gold the heroes are accompanying themselves with.
So, GMs, have you got that? Players enter town with chests or bags of goods. The Urchins should come up and ask, lots of questions, make them seem interested in what the heroes are brining home, what monster was killed and how much gold they've procured. As soon as the number is given, have the younger/dumber kids run off straight away, have the older kids ask more serious questions, make like they're not actually interested, maybe offer services or information on the town, have them very curious to look inside the adventurers purses..
Players will think they're going to be pick pocketed. Instead have all the money-lenders change their exchanges right away. No-body brings money into a city without 'paying' some kind of tax.
Which reminds me.. if your hero walks into a city with the same wealth of the city.. the king and his tax-man are going to want their share. if nothing less than to protect their currency rates. Just another money lender really, with bigger guards and bigger pockets.