The problem was proposed at CP‘96, and posted to comp.constraints by Jim Ho Man Lee on 22nd October 1996. The posting is archived at [CompConstraints96Posting].
The following paper studies different ways of modeling the Mystery Shopper Problem as a constraint satisfaction problem.
The following paper reports the application of E-GENET to solving the problem and the benchmark results [Lee98Local]
Increasing Constraint Propagation by Redundant Modeling: an Experience Report
Performance of a Comprehensive and Efficient Constraint Library Based on Local Search
11th Australian Joint Conference on Artificial Intelligence, 1998