It's a system you already use if you use credit cards. The payment processor play this role by assuming the counterparty risk and issuing chargebacks when they deem it appropriate.
Or for services/goods that requires this kind of leeway, use an escrow.
Yes it does introduce a third party, but the point is that compared to the current system there is no other option for the many cases in which you don't need don't want to use an escrow, the payment processor invariably act as such and can shutdown your business at will.