Because fraud is a constant threat when dealing with abstract concepts, merchants utilize specialized magical tools to ensure a transaction is valid:
The Scales of Intent: Found in major hubs like the Gilded Exchange and The Ledger Post. When a player attempts to barter a memory of "true love" to buy a magic item, the Fair-Brokers use a specialized water-scale. If the memory is shallow, fake, or a passing crush rather than deep love, the scale will read it as lightweight, and the merchant will reject the trade as counterfeit currency.
The Legalism of Gratitude: In this world, you never say "Thank You" to a fey merchant. Saying "thank you" implies you have accepted a gift and now owe an unspecified, open-ended debt. Instead, civilized travelers use phrases like "Our transaction is recorded," "My obligation is satisfied," or "Your kindness is logged."