Roland Perry wrote:
at 18:32:17 on Sun, 26 Feb 2012, Adam H. Kerman remarked:

UK credit card statements (including Amex) don't usually have
transaction numbers.

Ok. I bet the transactions are numbered, though.

Internally I expect they are, but the numbers are not revealed to the
cardholder.

What I was disputing was your retailer "two pass model", with the card
itself being authorised up to some "reserved" amount, ahead of the
actual amount being claimed milliseconds later by the retailer.

The card isn't swiped twice.

In a C&P terminal it's not swiped at all. "Inserted" would be a better
verb.

The merchants receives data in two steps.

You'll have to tell us what's in these two [rather than one] steps
(genuine question).

An alphanumeric Authorization Code is received. These are often printed
on receipts, so I know they are 5 numbers and a trailing capital letter.

In the second step, verification of the amount to be charged and the
transaction ID.

Some terminals used by the buyer require a number of steps:

1) Buyer swipes card; this can happen before or after the sale is totalled.

2) The authorization is sent after the card is swiped, which can be
before the final total is known.

3) Buyer is asked to verify amount.

4) Buyer is required to use signature-capture device if total amount
is over the amount set by the merchant to capture a signature. The
buyer is then required to touch the box on the screen to accept the
signature.

5) After buyer enters signature, cashier presses another button
to finalize transaction.

6) Transaction ID for final purchase amount is sent.

Depending on how busy the systems are, there can be noticeable delay
in receiving the authorization code. It helps to speed things up by
swiping the card as early in the transaction as possible.

I don't know why they'd do that, rather than ask for authorisation of
the actual amount first, because in the UK the amount has to be known
before you enter your PIN into the C&P device, as entering your PIN is
an agreement to pay that precise amount.

Uh, always? What do you do at a fuel station which requires a credit
card before dispensing fuel,

That's an exception, because of the way self-service pumps work (they
check the card first, then make the charge later).

or at a restaurant, when the tip amount to be charged is not known
until later,

In a UK restaurant you have to add the tip to the bill before contacting
the card company. That's not so very different from my experience in the
USA where they give you the bill, with an empty field for the tip, which
you hand to the waiter *filled in* (along with your card).

Sure, some restaurants in the US ask for the tip before swiping the card.
If the waiter takes the credit card, this seems to be uncommon. If the
cashier at the front entrance takes the credit card, they may ask
for the tip amount.

More typical: Bill is presented. Waiter takes credit card, swipes,
obtains authorization. Charge slip is presented to cardholder with a
blank line for the tip. A lot of times, the diner just leaves the slip
on the table and leaves without handing it to the waiter, and the transaction
may be finalized after the diner has left the restaurant.

The two-pass scheme is used in other circumstances, such as checking
into a hotel, when they often "reserve" an estimate of the final bill,
ahead of the day you eventually check out.

Ah. So the amount isn't always known. Do you provide the PIN
at that point, or not?

Yes. They appear to make a small charge (maybe ten dollars) which they
credit later, once the real amount of the "extras" is known the day you
check out.

Interesting.