Emanuele Quintarelli – Il Mondo
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Problem 1: Reputation Involves Costs and Needs Rewards
The eBay reputation system proves that if buyers are uncertain about seller’s trustworthiness, they will reward better seller reputations by raising their offers. Another aspect we must consider is that if it is costly to maintain a reputation for high quality (at least in time and effort), then a good reputation needs to be rewarded by the cost of building one. Similarly a bad reputation or a decline in reputation should incur a loss that exceeds the benefit from opportunistic behavior [7].
Reputation systems motivate people in ways monetary economies do. Any community that is equipped with a reputation system can truly benefit of a raise in its value only if the associated business model is capable to redistribute part of the extra value to the most valuable members of the community and the system provider.
Problem2: Avoiding Transferability of Reputation
In some rating based reputation systems it is to most raters’ perceived advantage that everyone agree with the rater. This is how chain letters, Amway and Ponzi schemes work [12,13]. They establish a system in which customers are motivated to recruit other customers.
As an example: If a vendor offered to discount past purchases if enough future customers buy the same product, it would be hard to get honest ratings for that vendor. All the buyers, in order to foster new selling and get the discount would rate the vendor very high.
Problem3: Verifying Assertions and Preventing Shilling
Among the simpler attacks that a reputation system can suffer the simplest yet very spread and dangerous, is called shilling. This term is often used to refer to submitting fake bids in an auction, but it can be considered in a broader context of submitting fake or misleading ratings, often exploiting identity forgery.
In particular, a person might submit positive ratings for one of her friends (positive shilling) or negative ratings for her competition (negative shilling). Either of these ideas introduces more subtle attacks, such as negatively rating a friend or positively rating a competitor to trick others into believing that competitors are trying to cheat.
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