"Mystery shopping" refers to a practice where people are hired to act like regular customers and secretly evaluate the quality of service provided by a business. Full definition
In general, you want a company with experience in conducting mystery shopping in your industry and your type of business. (inc.com)
They offer a ton of mystery shopping jobs for clients in banking, oil & gas, home improvement, cell phone, and other retail businesses. (earningmytwocents.com)
I do mystery shopping once in a while but only if it's convenient. (makingsenseofcents.com)