Bitcoin Forum

I'm talking for check out counter transactions, and the network needs to agree it's correct.

Because 10 minute block size and 6 blocks needed for a confirmation seems like it can't be good enough.

I have heard the poll the miners approach.. how quickly can that be done?

There's no absolute, it's just degrees of risk, going from 0-confirmation to 100 blocks of confirmation or more. I'm not aware of any theory or paper trying to quantify those risks precisely though, it's actually pretty difficult. I'd be interested if someone knows of a good publication here. If someone gets a good risk profile, I can imagine an insurance business could get structured around it.

Retail point of sale can happen with just transaction, 0 confirmations, which takes only seconds.

If people don't wait for confirmations then what prevents me from creating a double spend app that let's you double spend your Bitcoin?

You could build such an app.  It would work some of the time.  You could also
simply walk out of the restaurant without paying.

This topic has been discussed in many threads. Here's one
https://bitcointalk.org/index.php?topic=159994.0

The same thing that prevents every other form of fraud and theft.

The morality and ethics of the majority of your customers, and the theft and fraud laws that allow you to catch and prosecute those without morality and ethics.