Force used when lifting is a problem? (5,10)

I believe the answer is:

store detectives

I'm a little stuck... Click here to teach me more about this clue!

'lifting is a problem?' is the definition.
I can't judge whether this defines the answer.

'force used when' is the wordplay.
I cannot really see how this works, but
'force' could be 'e' (E is the symbol of electromotive force) and 'e' is found in the answer.
'when' could be 'e' (I've seen this in other clues) and 'e' is located in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Sunday Times.

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