“…Indeed, different cultures, different habits and different preferences complicate this problem and data are often unavailable [12]. Different proposed approaches [13,16,15,5] try to address this challenge. In particular, in [16] the trust is explicitly defined as a trust network which correlated two different users and is propagated to all the users in order to predict, how much an user could trust every other user; while in [5], the concept of trust is evaluated by means of shopping cart of the customers, so that users with a similar desired product are trustworthy.…”