On 26-Feb-12 11:24, Roland Perry wrote:
In message , at 10:50:46 on Sun, 26 Feb
2012, Stephen Sprunk remarked:
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.

Hotels are the most obvious example, but restaurants with waitstaff do
the same thing: they will authorize the card for the subtotal (price
plus tax) plus a liberal estimated tip (eg. 20-25%). Either way, the
actual total isn't submitted until the transaction is
posted--potentially several days, not "milliseconds", later.

The "milliseconds" scenario is when I'm buying hardware from a store,
and am standing at the checkout.

A hardware store is not a hotel or restaurant. You snipped the relevant
response:

Most other merchants authorize for the exact total, since it is known as
soon as the purchases are rung up.

There are still two steps: the merchant gets authorization at the time
of purchase and then posts the transaction at some later time,
potentially several days later.

You may not be _aware_ of the second step, but it's there.

S

--
Stephen Sprunk "God does not play dice." --Albert Einstein
CCIE #3723 "God is an inveterate gambler, and He throws the
K5SSS dice at every possible opportunity." --Stephen Hawking