[sjs1234]

If I understand correctly the independent third party is only needed in a dispute. If the buyer and seller are happy then completing the transaction does not require action by anyone else.

This delays payment until 2 of the three parties sign off. From the buyer's point if view that is reversibility. From the sellers point of view this is a delay in getting paid.

[the_mitsuhiko]

People complain that PayPal freezes merchants accounts. But PayPal only does that if the number of unsettled goods is too high. In this particular case it would always happen because parties would not acknowledge a transaction for a long time.

Chargebacks allow a merchant to get the money right away and still give the customer the option to reverse the charge a month (or more later) in case something happens.

[nadaviv]

Could the money really be considered the merchant's if PayPal can still come later and take it back?

[the_mitsuhiko]

PayPal does not come back later, that's the point of paypal. PayPal hedges against chargebacks and handles them itself. In case thinks you're above the average risk, it will start freezing your account temporarily. But they will never come back after 180 days and want your money.

On the other hand if you sell directly via credit cards, the credit card company can come to you after 180 days and want money back.