This is a quote from the book "On Zero Confirmation Transactions" by Chris Pacia
...ose to zero.
read full book
But why all the fuss about about unconfirmed transactions? While most Bitcoin users can afford to wait an hour for their payments to confirm, there are some business mo
dels which cannot. Retail is the most obvious example. Customers need to be able to pay the cashier and leave the store instantly. They can’t be required to wait around for 10 minutes or longe
r for their transaction to confirm. If retailers are unable to mitigate the risk of fraud when accepting unconfirmed transactions, then they simply wont accept Bitcoin.