While making purchase, it is important that currency is not volatile.
If a person purchased a good of $ 10 and receives $1 worth tokens at that time.
He goes to another shop after one year, and he finds out that tokens are now worth $0.5 only. This would not be good for customers as they would be at risk fictions price.

So how would you prevent such situation?
Correct me if I'm wrong somewhere in my assumptions.