Super-duper shop is dropping purchases? (4,6)

'super-duper shop is dropping purchases?' is the definition.
I can't judge whether this definition defines the answer.

'shop is dropping purchases?' is the wordplay.
I cannot really understand how this works, but
'shop' could be 'mart' (I've seen this in another clue) and 'mart' is found within the answer.
'is' is present in the answer.
'dropping' could be 'scat' (I've seen this before) and 'scat' is located in the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?