Do you mean instant confirmation? I think you have never heard about greenAddress, it is a web wallet with an instant confirmation (the only rule is that also the other part uses it). Now it can be used for any payment processor.
I used to use green address until after an update it stopped working altogether, another update later and it's back working but slow as to open, it's empty now so i won't be using it again.
Has someone got a quick explanation of how instant transactions work.
An instant transaction wouldn't really be "instant" it was just be "instantly trusted" by those in the network. It could work like this:
A multibillion dollar company establish good rapport in the community and acts as a middle man. Each of us has a "bank account" with them in which we keep some fraction of our bitcoin. This huge/trusted company has 1 well known public address. We walk into a store and use our app that is run by this company, we scan the stores QR code and the bitcoin is sent to the store from that well known public address on our behalf, then the well known company deducts that amount of bitcoin from our "bank account" with them.
The store then sees that the payment came from a well known/regulated/large company and that they "are good for it" meaning that they will not try to create any double spends, thus the transaction is still on the bitcoin blockchain and the transaction is "instantly trusted" by the store, allowing the store to then give the customer the goods with confidence that there will be no double spend and thus no need to wait for confirmations.
a way to do it without trusted parties is just query other nodes in real time for any attempted double spends. (see BIP 35)
