A secret-shopper initiative run by Diamond Comic Distributors last year detected 50 cases of stores selling comics before their advertised street dates. That's more or less in line with the 98 percent compliance rate Diamond found when it launched its day-early delivery program in 2011, according to ICv2's analysis.

Yes, Diamond has secret shoppers.

Some retailers pay Diamond a $4 per week stipend for the benefit of receiving books a day early. Diamond started that program to help stores have a one-day buffer in case holidays or bad weather delay a shipment. It turns out to make the program work, secret shoppers were hired.

Penalties for breaking a book's street date include suspensions of the day-early delivery service or, if a store violates the policy enough times, being barred from the program entirely. The report didn't include a list of offending stores or details about whether the offenses were intentional or merely accidental.

[Via ICv2]