Sister-Logic

Problem/Situation:
Three different individuals, A, B, C recently had their air conditioning serviced and/ or replaced.
A paid X.  B paid Y. And C got an estimate for Z.
Z>Y>X


What conclusions can we draw?


My sister's suggestion:  C got (or was going to be) cheated.


My suggestion:  Did A, B, and C have exactly the same thing done?  Did each purchase exactly the same unit?


My sister's reply:  "I am not talking to you.  You are impractical."
QED


The reader should feel free to supply missing steps and formalization.


After-thought:
And what if Z is twice as much as X?


Reply:
You still need to know whether C purchased/was planning to purchase the same thing as A.