-snip-
It's not the technical aspects of irreversability that I'm concerned of. Perhaps it's more the anonymity combined with lack of legal endorcement.
Let's imagine a world where a) bitcoin is legal form of payment and b) Every user can be associated with the addresses he/she owns. Then in a transaction I can ask for legal protection and the law could force the cheating party to send back a payment.
But this is obviously not the vision of bitcoin.
It's easy for law enforcement agencies to link Bitcoin addresses to an individual, let alone if said individual is running a business online.
Assuming a platform like Ebay, where they would most likely use BitPay for Bitcoin payments, a seller could be easily identified since he'd be using both of those platforms.
At the end of the day it's up to the user to make safe purchases. Bad customer experiences are reflected upon seller feedback and they're bad for business, so sellers will have to do their best to satisfy their customer.
Think about it another way, how many times have you tried to reverse a transaction through PayPal or bank because of something that was
completely beyond your control?