The main drawback of this rating is people will create sockpuppet and false trades to stay in the top 10. See how CanaryInTheMine is abusing DefaultTrust. He is adding those to his trust list, who is leaving him +ve feedback and thereby having a huge green signal. Same will happen for these decentralized arbitration systems. It can not be trustless, if it is manual.
Yes, as the OpenBazaar paper says, this is the main thing that needs to be addressed:
"In decentralized systems, Sybil attacks [Douceur] make this situation particularly more challenging and without an easy way to resolve."
They go into a lot of different options to address it including proof of burn.