Peer-to-peer complementary currencies can be powerful tools for promoting collaborations and building relationships on the Internet. i-WAT [1] is a proposed such currency based on WAT System [2], a polycentric complementary currency using WAT tickets as its medium of exchange. Participants spontaneously issue and circulate the tickets as needed, whose values are backed up by chains of trust. i-WAT implements the tickets electronically by exchanges of messages signed in Open PGP [3]. This paper clarifies the trust model of i-WAT, and investigates how it is related with that of PGP [4]. To implement the model by dynamically building an appropriate web of trust (WOT), we claim that it would suffice if the behaviors of participants satisfy the following three properties : 1. mutual signing by knowing, or any two mutual acquaintances sign the public keys of each other, 2. mutual signing by participation, or the drawer and a user of an i-WAT ticket sign the public keys of each other, and 3. mutual full trust by participation, or the drawer and a user of an i-WAT ticket fully trust each other, and a recipient fully trust the corresponding user of a ticket, in the context of PGP public key signing. Likelihood of satisfaction of these properties is supported by the (dis) incentives imposed by the semantics of i-WAT. A reference implementation of i-WAT has been developed in the form of a Jabber [5] instant messaging client. We are beginning to put the currency system into practical use.