When is a customer removed from the Dynamic Remarketing list?

A customer is removed from a Dynamic Remarketing list when they purchase a product because the goal of remarketing is to encourage conversions. Once a purchase is made, the immediate goal for that specific product is achieved, and continuing to show ads for an item they already own would be inefficient and potentially annoying. Viewing, adding to a cart, or searching for a product are all actions that indicate interest but do not fulfill the conversion goal, thus keeping the customer on the remarketing list to encourage them to complete the purchase.