Can some briefly explain how Dash's instant transaction work?
Does the receiver get the "same" Dash that are sent? Or does someone else give the receiver "other" Dash from "somewhere else"? Or do they get a credit awaiting confirmation?
The receiver gets the same Dash, the best analogy I have found is that an InstantSend lock is like a certified check, you still have to "cash" it on the next block, but is "locked and certified" by the network so you can act on it the moment you receive it and give the goods and services to the buyer without having to wait.
Read this:
https://dashpay.atlassian.net/wiki/display/DOC/InstantSend