A few years ago, GoPro was grappling with an exasperating problem: Unknown sellers were offering stolen GoPro cameras on Amazon.com at a discount.

While the stolen items accounted for only a small percentage of GoPro’s total sales, the discounting created a domino effect as competitors tried to match the low price. Amazon would first cut its own price, then retailers like Best Buy and Walmart would follow, according to four people with knowledge of the situation at GoPro. The thefts, they said, undermined GoPro’s pricing strategy.