## 4 Presentation and Discussion of the Results
### Research Outcomes  
In Section 3.1, we formulated our research questions. After presenting and discussing the selected works, we will now try to answer those questions.  
_(i)_ _Do current architectures provide guarantees of transparency and immunity to attacks and fraud?_  
According to the literature, the current reputation systems, centralized or decentralised, suffer from several limitations: (1) They are managed by one entity, which does not give all guaranties of transparency. (2) They are isolated systems that do not share the reputation data, therefore, a user or product may have distinct reputation scores in each platform. (3) The identity management is not effective, thus, enabling Sybil and white-washing attacks. (4) Since the reputation data are not shared by the e-commerce platforms, it is harder to combat common fraud types, i.e., ballot-stuffing and bad-mouthing.  
Based on these findings, our answer is no, the current architectures do not provide guarantees of transparency and immunity to attacks and fraud.  
_(ii)_ _How are these limitations being addressed in blockchain-based architectures?_  
As proposed in the literature, two major approaches exist based on: public blockchain networks [16, 18, 19, 40, 44] and permissioned networks in consortium [41, 42]. The first approach is supported on economic viability, in which it is not economically viable to be a dishonest user, and honest users are rewarded. In the latter approach, the e-commerce platform is accepted in a consortium by agreeing with a set of rules. Typically, there is a central agency that manages the consortium, as well as a central management of user identities and digital certificates.  
Regarding the vulnerabilities in identity management, the literature proposed two approaches: (1) costs in creating new identities and (2) a central authority. The approaches both intend to ensure that an entity has only one user on all platforms, thus, mitigating the Sybil and whitewashing attacks, in general, by linking the user in the e-commerce platform to his address in the blockchain network.  
In short, in blockchain-based systems, the reputation model formulation could be more effective when deriving the reputation scores, mitigating the common types of fraud, i.e., ballot-stuffing and bad-mouthing frauds. By means of economic models that apply costs to operations and financial incentives such as rewards, or financial penalties to dishonest users, one could improve the model's performance. Community-driven approaches are also proposed, in which users validate the feedback from other users. In addition, one can find other proposals in the literature for inputs based on direct and indirect observations, such as the human behavior and psychological factors [38, 39], inferred observations, as well as ageing mechanisms [38, 39, 41, 44]. However, these blockchain-based models do not guarantee that false, unfair, or biased reputation data enters into the chain.  
The blockchain paradigm, due to its properties of decentralization, immutability, and tamper-proofness, provides the conditions to mitigate the aforementioned limitations present in the current approaches to reputation systems. One fundamental problem is the lack of trust among the entities that manage e-commerce platforms. The blockchain may be the means to archive this desirable trust, in which all participants can share their data in a decentralized, tamper-proof, and transparent way, but it does not solve the problem of the blockchain oracles [26, 27, 28, 29]. Finally, there is also the significant challenge of global adoption of that blockchain network.  
_(iii)_ _What are the proposed Blockchain-Based Reputation System Architectures?_  
In Table 2, we present the list of the proposals that we found in our systematic literature review. As far as we know, these are the most recent and relevant works in the field of blockchain-based reputation systems, in different stages: proposal, model, or prototype.