Bitcoin-otc is a peer to peer (over-the-counter) marketplace for trading with bitcoin crypto-currency. To mitigate the risks of the p2p unsupervised exchanges, the establishment of a reliable reputation systems is needed: for this reason, a web of trust is implemented on the website. The availability of all the historic of the users' interaction data makes this dataset a unique playground for studying reputation dynamics through others' evaluations. We analyze the structure and the dynamics of this web of trust with a multilayer network approach distinguishing the rewarding and the punitive behaviors. We show that the rewarding and the punitive behavior have similar emergent topological properties (apart from the clustering coefficient being higher for the rewarding layer) and that the resultant reputation originates from the complex interaction of the more regular behaviors on the layers. We show that the systems' reputation inequality reaches a high steady value with the network evolution. We characterize the reputation trajectories identifying prototypical behaviors associated to three classes of users: trustworthy, untrusted and controversial. Controversial users are the only ones presenting up and down reputation trends. We focus on these cases for understanding which are the possible factors driving reputation falls and which dynamical patterns characterize these cascades: some users have real oscillating behaviors, other abuse of the trust system doing a few good transactions to gain reputation for cheating the users afterwards, other naturally and slowly die out after a long series of positive exchanges (like disappearing from the system) and finally, some users are hardly beaten by organized trolling attacks.