Any decentralized system which is not purely trustless will be inferior than centralized trust systems. The reason of bitcoin's success is not only that it is decentralized, but also it is trustless. All these efforts like Bitsquare.io or OpenBazaar has failed to be purely trustless and relying on an arbitrator. IMHO, as soon as you bring in human interference you are no more trustless and just a flavor of centralized trusted systems.
But the arbitrator is decentralized. Anyone can become an arbitrator, all they are doing is confirming a transaction just like a mining computer would confirm a transaction.
What happens when they get it wrong from time to time or even become scammers themselves? Any issue with trust and a feedback system is a tricky business. Just look at ebay. It works well when you are scammed but it can also easily be abused by fraudulent buyers. It's going to be interesting to see how these decentralized markets handle this stuff as it could be make or break.