mystery shopper - definition and synonyms

noun [countable] 

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/ˌmɪst(ə)ri ˈʃɒpə(r)/
singularmystery shopper
pluralmystery shoppers
  1. someone who is paid to visit shops, restaurants and other businesses pretending to be an ordinary customer in order to find out how good the service isThis meaning is based on one submitted to the Open Dictionary from United Kingdom on 13/04/2015