A brief introduction to those who do not know about the anime/light novel franchise, in a certain arc Holo-chan and Lawrence found out about a currency devaluation scheme in which a certain kingdom devalued the silver purity of its currency to gain profit, and gave royal privileges to merchant companies who would bring back the older coins which have higher purity than the new ones.
There was also scamming going on, in which a rival company had a scheme that they would tell people the value of the new currency will increase, when it is actually going down so people would exchange the old ones (worth more) for the new ones and the company would gain profit.
Historically, how common or did such similar practices occur in the economy of Medieval or Renaissance Europe, the time period Spice and Wolf is set in?
I can't speak for every country, but it certainly doesn't fit what happened at the Royal Mint of England. The records of the mint go as far back as the 12th century. At first the mint went with fixed weight coins (i.e. always the same amount of gold and silver in each coin) but then in 1344 a reduction in the gold and silver content of coins occurred (i.e. devaluation). After this we see a pattern of exchanging old coins for devalued coins on average about once in a generation. The mint had begun devaluing coins out of necessity, not profit motive, because they had discovered the drawbacks of a fixed weight arrangement. You have probably heard of Gresham's Law, that bad coins crowd out good coins. In pop economics this is usually treated as a reason why it's a bad idea to start issuing devalued precious coins. But what people don't realize is that old coins also go bad over time. Not only do they gradually get worn down, they even suffer from clipping, the practice of cutting off small pieces from a coin in order to essentially steal a tiny amount of gold or silver. In other words, the nominal value of an old coin no longer matches its precious metal content because of deterioration. Therefore some form of adjustment is necessary to avoid the negative effects of an increasing divergence between coins of varying age and amount of wear and tear. Hence the generational exchange and concomitant devaluation of coins.
The mechanism for getting old coins out of circulation was usually pretty straightforward. The mint simply posted a price at which it would buy a certain amount of bullion (bars or ingots of gold and silver) for a certain amount in new coins (the new coins having about the same precious metal value as old worn coins). So if you sold a kilo of gold to the mint you'd get, say, 100 gold coins before the devaluation and 110 coins after the devaluation. There's still a kilo of gold in both the 100 coins and in the new 110 coins so the seller does not feel cheated (I'm glossing over issues of seigniorage to simplify the point). This practice established a floor for the price of precious metals, in other words there was little point in selling to somebody offering less money. This floor also helped stabilize the monetary system. Note that this system does not preclude wild swings in the price of goods. For example after a bad harvest year a silver coin might buy a bag of flour, but after an abundant year when the market is flooded with wheat the same coin could buy two bags. All the system does is peg the value of coins to the value of precious metals.
Note that an alternative method for removing old coins from circulation without somebody feeling cheated would be for a country's treasury to subsidize the buying of old coins.
Source: https://voxeu.org/article/medieval-monetary-practices