As far as I can see, the essential problem with decentralized anonymous marketplaces is that reviews need to cost money. Plain and simple. Good reviews have great value, so they need to have a non-zero price. A vendor's review history is the indicator by which you assess whether a vendor is trustworthy or not, and a vendor should have to pay to achieve a trustworthy reputation - if good reviews are free, and you can make money from good reviews, they would have little value.<p>This is the reason spam emails are so frequent: you can make money from something that costs very little. If reviews were near-free, good reviews would be as plentiful as spam emails.<p>Free reviews means vendors can make sock-puppet accounts, fake a transaction, and leave a five-star review to themselves. With Silk Road, they take <i>x</i>% of the value of each transaction (or if not, that's at least how it should be), so if a vendor seeks to inflate their review score, they will pay a price for it.<p>In fact, a good overall review score for a vendor - as far as I can tell - is the sum of all the review "values" (1 to five stars) multiplied by the value of the transaction in question. So a vendor with 10 five-star reviews on 10 orders of a value of 1 BTC each, would have the same score as a vendor with a single five-star review on a single transaction with a value of 10 BTC. Both these vendors would have paid the same amount of money to get this, equal, review score.<p>I've thought a bit about this, and I don't see how this can be solved in a decentralized market, with no middleman to tax transactions, and make sure that vendors can't get free reviews.