Pursuant to MCL 600.2953(1):
Quote Quoting MCL 600.2953(1) - Civil Demand for Shoplifting
In addition to applicable penal sanctions, a person who commits an act for which he or she could be charged with retail fraud in the first, second, or third degree under sections 356c and 356d of the Michigan penal code, 1931 PA 328, MCL 750.356c and 750.356d, is liable to the merchant who is the victim of the act for the full retail price of unrecovered property or recovered property that is not in salable condition, and civil damages of 10 times the retail price of the property, but not less than $50.00 and not more than $200.00.
Given the circumstances you describe, I would have been wary as a merchant of engaging in the sort of strong-arm, on-the-spot demand, out of concern that the situation would start to resemble one of extortion. But a civil demand is legal against shoplifters in Michigan.