Dysterio's Alchemic Wonder

The darkest mysteries of alchemy have always existed just beyond the grasp of our draconic overlords. The giants guarded these secrets within their practice of Garonis magic, the best source of alchemic powers. However, I have recently discovered ruins of a giant alchemist's workshop and documented all their secrets into my trusty journal. The notes are my own (hehe), but I will graciously share one recipe I created as a result of my findings.    

Fool's Gold (Alchemic Recipe)

Ingredients

• Organic tissue (bones, flesh, etc.) of a giantoid
• A powerful hallucinogen
• Tears of a reptile
• 30 GP

Output

10 GP of Fool's Gold, which functions as regular currency with the following properties:

• When spending 1 GP of Fool's Gold, the spender can cast an illusion that this amount of gold covers the entire cost of the purchase
• Illusion can be combated by the merchant with an Intelligence saving throw (DC equal to the spender's spellsave DC, or 8+proficency bonus+Charisma modifier if they aren't a spellcaster)
• All characters on the merchant's side of the transaction pass or fail based on the roll of the lead merchant
• Illusion wears off after a day