Yes, that's why it's a big problem. They also often make the wrong decision and leave people screwed over. Just look at all the complaints from Ebay sellers who got ripped off by Ebay siding with the fraudulent customer. There are cases where the seller can't trust the buyer and the authorities that are supposed to be arbitrating disputes can't be bothered doing their job because it's too hard. That's where crypto's non-reversibility is useful.