I have been thinking about how one would create a safe marketplace that handles disputes fairly - let's just say I want to be a part of a safe one hence maybe I might want to create one.
One of the issues I've come up with is how does one handle a dispute when a buyer of an item claims the item is faulty or not as described and wants a refund, but the seller is quite confident the item is working and nothing affected the items on delivery.
In most jurisdictions, the buyer has statutory rights -- they should be able to return an item for a full refund even if it is not faulty, for a period of 30 days or so. This might cost the seller somewhat (wasted time, shipping fees etc.), but they should price this into their business -- all sellers have to deal with it. The Bitcoin community isn't immune from this.
The best thing you can do is encourage sellers to live up to their statutory obligations (unless there's a good reason (e.g. digital goods) why they can't), and encourage users to rate accordingly. Sellers with nice return policies (e.g. 30-days no-questions-asked) will do brisker business than those who will enter into an online tiff when the buyer states the items were damaged.
Another issue I've thought about is how does one prevent scammers from a marketplace aside from relying on user ratings/ratings ( which could be skewed from people wanting to boost their ratings by making duplicate accounts). One thing I thought about is requesting more information aka driver's license or some type of way to background check a person.
If anyone could chime in with systems already in place I'd appreciate it. Also if anyone has other issues they've seen which weren't able to be handled correctly, please describe them here. Thanks and appreciated.
Most ratings systems are based on the number of transactions rather than the number of users. Sock puppet accounts shouldn't have any bearing on that? You could also do a pagerank-style algorithm, where feedback from users with high feedback themselves is rated higher than newbies -- but you'd have to monitor it carefully to avoid cronyism.
Hope that helps :-)