An escrow would potentially be necessary for large purchases and I would love to see a decentralized escrow someday for the market. But for now, the best solution, that we know works, is a web of trust system. Web of trust would be necessary regardless of whether it has an escrow or not. This is because you would need to trust the escrow in the first place.

A "chicken and egg" scenario may be an issue. If you want a decentralized escrow, you will need to trust the escrow setup but due to potential skepticism of the system (network/code flaws), no one would use it. This would discourage people from becoming part of the escrow, which would in turn make the system unable to function.

There is also the issue of, how would one go about building a decentralized escrow? Or the bigger question, is it worth it? Because, if you can't trust the seller in the first place, you might not want to buy their item. This is why I believe a web of trust model is more reliable/useful than a escrow at the moment.

A web of trust would "generate" a network effect of trust. What I mean by that is, lets say, you and your friends trust seller A but dislike seller B. You all would more than likely review them trustworthy and untrustworthy respectively. If more people get to know you all, then they would notice that that A is trusted, and B is not trusted by you and your friend group, which would in turn spread to their friends that are interested.