Filter measure

Hey, 

Is the Description column unique to each purchase / refund? If so, you could do something in DAX like:

SWITCH(TRUE()
    CALCULATE(COUNT(description), ALLEXCEPT(Table, [Description]) > 1 &&
    CALCULATE(SUM([Transaction Amount]), ALLEXCEPT(Table, [Description]) > 0, "Partial Refund", 
    CALCULATE(COUNT(description), ALLEXCEPT(Table, [Description]) > 1 &&
    CALCULATE(SUM([Transaction Amount]), ALLEXCEPT(Table, [Description]) = 0, "Full Refund", 
    BLANK()
)

To explain the logic behind the code - the COUNT(description) looks if the same product has 2 entries (assuming that each description is unique, then if the person purchases another of the same product, then there would be some kind of increment counter in the description. This is a massive assumption though). And then summing the amount - if it's a partial refund, then the amount paid should be greater than the amount refunded, hence the >0 condition.

Hope that makes sense.