Surprise regarding 50% refund (7)
I believe the answer is:
astound
'surprise' is the definition.
(to astound is to shock or surprise)
'regarding 50% refund' is the wordplay.
I cannot really see how this works, but
'regarding' could be 'asto' (as to that topic...) and 'asto' is present in the answer.
The remaining letters 'und' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for astound that I've seen before include "floor" , "Bewilder" , "Amaze, astonish" , "Flabbergast" , "Fill with wonder or astonishment" .)