I'm an employee at a car rental agency in the US. I'm writing a
training handbook and am working on the section regarding credit card
authorizations.

How long do credit card holds (i.e. "authorization only" transactions)
last before they expire?

I know there is great variance. I've heard that they last for 3 days,
7 days, 10 days, 30 days or that it depends on the issuing bank. I've
heard that offline debit cards (check cards) hold them for a maximum
of three days, and I've also heard that VISA implements a more complex
system in which the hold expires at the end of the rental (somehow the
computer system transmits the expected return date with the credit
card authorization, I guess).

I've spent the last two hours searching the Internet and I can't find
any concrete information on expiration times. I'm looking for more
concrete information.

Sources I've checked:
http://www.visa.ca/en/merchant/pdfs/carrental_tips.pdf (it's for
Canada, but the physical brochure I have for the US is nearly
identical)
http://www.tax.state.ny.us/evta/guidelines_credit_authorization.htm
(this page, under "Valid Authorization Timeframes," alternately
implies both that authorizations are valid for 3 days and also for 30
days)
http://www.shift4.com/insight_debit.cfm (details a couple of the many
reasons hotels and car rentals don't accept debit cards for deposits)
http://www.visadps.com/serv-authproc.html (apparently for banking
institutions: says that "Hold length is parameter-driven and can be
set at the financial institution or transaction code level."
http://euro.ecom.cmu.edu/resources/elibrary/everycc.htm (outdated, but
limited helpful information in the couple paragraphs starting with "An
account typically has a credit limit..." about halfway down)

Other sources I plan to check if I can't get this solved:
Global Payments' help desk at 1-800-467-2638.
Our local bank/credit card processor
Our computer software vendor--it's server-based out of state, and they
handle the interconnect between our credit card processing and the
system

Last, I've set the price for this answer fairly low because I'm really
just looking to see if someone knows this off the top of his or her
head. If not, then I might up the price later if I'm unable to find
the information out myself.

This will probably depend on where the card was issued.  For cards
issued in Norway, "credit card holds" cannot be held for more than 10
days.  The card holder may cancel a "authorization only" transaction
at any time by contacting the card issuer.

My comment above relates to Norwegian DEBIT cards (such as Visa or
MasterCards thata are tied directly to the owner's bank account), not
"true" credit cards.  Sorry!

Interesting. I'm not sure what the laws/policies here in the States
are regarding canceling a hold. I know that in general, we can cancel
a hold by calling the number on the back of the cardholder's card.
Unfortunately, there's no uniform outcome: sometimes we can't get
through, sometimes the agent will refuse to speak to us unless the
cardholder is present, sometimes they won't understand what you're
asking for, and other times they'll make you go through hoops like
faxing or (gasp!) mailing them a written request.

Our new computer system allows us to perform authorization reversals
on VISAs (because of their more sophisticated system), but MasterCard,
American Express and Discover still require the manual method.
Fortunately, most people have enough available credit that they don't
make a big deal of it.

One other (unrelated) note about international cards: it's often
confusing when working with foreign cards. I recently had some renters
rent on a VISA Electron card from the Czech Republic. I balked at
first because the card did not have embossed numbers (meaning it
couldn't be imprinted, and we can lose a chargeback if the card is not
imprinted, even though we swipe and authorize it electronically).
Eventually I determined that the VISA Electron
(http://international.visa.com/ps/products/electron/) was simply
designed to only work with on-line authorizations and not with manual
credit card imprinters like old businesses used to use. I found out
later that it was actually a debit card, which we normally don't
accept. No big loss, but a bit of confusion on my part.

Hi jclutch

I happen to work in a Card Centre.  You cannot search the answer in
the web because the Card Associations do not impose any regulations on
how long an issuer should 'hold' an authorization.  Different issuers
(banks) have different practice.  According to my understanding they
range from 3 - 14 days, that usually depends on the bank's policy -
whether they are more customer-oriented or more conservative in taking
risks.

Actually you do not need to call the issuing (your customer's) bank to
cancel an authorization.  This should be done through your acquiring
bank so it only takes you one phone number to remember.  They should
contact the issuing bank on your behalf (Actually issuing bank won't
deal with merchant directly)and talk straightly to the Authorization
Centre.  Of course automation saves you and the acquiring bank lots of
manual work, that's why they provide you with a system capable of
reversing an authorization.