Grab a customer pinching calculator (6)
I believe the answer is:
abacus
'calculator' is the definition.
(abacus is a kind of calculator)
'grab a customer pinching' is the wordplay.
'pinching' indicates the answer is hidden within the clue (the clue has stolen or pinched the answer).
'ABACUS' is hidden in the letters of 'grab a customer'.
(Other definitions for abacus that I've seen before include "Basic calculator makes" , "Counting device" , "Early counting-frame" , "An old counting frame with beads" , "one counts on it" .)