In this paper, we discuss a peer-to-peer (P2P) based fully distributed system where each peer process autonomously makes a decision by itself using information obtained from its acquaintance peers without any centralized coordinator. An acquaintance of a peer p is another peer about whose service p knows and with which p can directly communicate. Here, it is critical to discuss how much a peer can trust each acquaintance peer. In this paper, the trustworthiness of an acquaintance peer is defined in terms of the satisfiability and ranking factor with confidence. The trustworthiness depends on how much a peer is satisfied by an acquaintance for each service request and how much each acquaintance peer is trusted by others, i.e. satisfiability and ranking factor of an acquaintance, respectively. In addition, it is significant to discuss how confident a peer is of its own information, satisfiability and ranking factor of an acquaintance. We present a simple auction system as an example in this paper.