A store detective is someone who is employed by a shop to walk around the shop looking for people who are secretly stealing goods.
store detective in British English
(stɔː dɪˈtɛktɪv)
noun
a person employed by a shop, particularly a department store, to watch for shoplifters and gather evidence, apprehending thieves when necessary and liaising with the police and store manager
Examples of 'store detective' in a sentence
store detective
If I were a store detective, I'd never have let me out of there without a body search.
Val McDermid DEAD BEAT (2002)
But I let the store detective lead me away, leaving Peggy with her new protectors.
Tony Parsons MAN AND WIFE (2002)
Then suddenly there was a store detective, all brown shirt and shaven head and biceps.