I have seen questions regarding fake reviews that give glowing appraisals for products or services which are paid for by the companies that provide those products/services (or by the marketing/PR company that they paid), and this is one of the issues with review systems.
What about the opposite scenario of people who deliberately seek to damage the reputation of their competitors by writing bad reviews? Is it actually just as easy to spot a damaging review that is either not from a genuine customer or by someone who is exaggerating the facts because they want to vent after their expectations were not met? What are the strategies that can be used to reduce the impact of these types of reviews?
On a related topic, do 'bad' reviews really have the effect and impact intended on review systems? I saw an interesting question about prices at an overseas restaurant in another StackExchange site where someone thought they were being overcharged, and the restaurant in question didn't have a very good rating yet people still don't seem to consider checking the ratings (or if they did it didn't prevent them from visiting for whatever reason).