"The ambiance of the store invites multiple purchases, " adds expert Elaine Buxton, president of the Mystery Shopping Providers Association.

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According to the Mystery Shopping Providers Association (MSPA) there are some 30, 000 of them in the U.S., hired by luxury hotel brands to check-in anonymously and judge mercilessly.

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Additionally, there are industry organizations, such as the Mystery Shopping Providers Association, National Association for Retail Marketing Services, and International Association of Service Evaluators, where shoppers can view directories of member companies.

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