About to happen where shoppers may be seen (2,5)

I believe the answer is:

in store

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'about to happen' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for in store that I've seen before include "within retail site?" , "stocked" , "Approaching" , "Awaiting delivery" , "Soon to happen" .)

I've seen this clue in The Independent.

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