Product configuration is a well-known technique that allows safe and reliable customization of products in assembly to order (ATO) or make to order (MTO) industrial situations. When dealing with engineer to order (ETO) situations, the required design activities cannot be handled by conventional configuration techniques. The first goal of this paper is to show how constraint based configuration techniques can be extended towards ETO situations for both product or system and their realization process. As ETO situations requires some design activity, the confidence in the configured item or offer proposed to the customer is lower compared with ATO-MTO situations. The second goal of this paper is to propose a set of indicators that characterize the confidence of the supplier in the configured system and process and therefore in the offer provided to the customer.