Not in every case, for sure. But many cases are pretty easy to arbitrate. This one for example: when the transaction fees 230× greater than the transaction amount, it is fair to assume that is was not meant to be that way. If I loose my credit card and/or it gets stolen, and someone uses it in the time between when I declare I lost it and when it is blocked, my bank is required by law to refund me (and I guess my bank attempts to get their money back too, but that's not really my problem).

Also:

> There's fraud where people buy an item online, then claim they never received it and get their payment refunded while keeping the item.

A blockchain can't solve that kind of problems. And it never will. It is not because something is written on a blockchain that it is true, except for cryptocurrencies because that is how they define truth. But as soon as you have something happen in the real-world (in your example, an item sent in exchange for a payment), then a blockchain is useless, or at least, it is not any more useful than any type of ledger.