QUOTE(cljohnr @ Mar 10 2006, 02:52 PM)

I've never seen anything to indicate that this is a violation of CC policy. Often, the CC processing terminals automatically do it. The restaurant may not even know.
http://www.bankrate.com/brm/news/cc/20010821a.asp...
"Holds occur any time the end amount of a purchase is not known at the time a card is authorized," says Kenny Thomas, director of corporate relations at Visa U.S.A.
...
"The hold is released as soon as the final transaction is cleared and that's usually within 24 hours," Thomas says. "Visa policy requires merchant holds last no more than 72 hours after the final transaction takes place."
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"If a hold causes them a problem, they should discuss that with the issuing bank and ask them for relief on the fees," Thomas says.
It is true that quite often a restaurant's machine may be pre-programmed and they may not even know, but it is still a violation. It is indeed against the rules to authorize for more than the price at a resturant. This is from the merchant agreement as posted at the link on www.usa.visa.com.
QUOTE(from VISA Merchant Agreement)
Numbered pages 10 and 11 of the merchant agreement have the following:
Dollar Minimums and Maximums
Always honor valid Visa cards, in your acceptance category, regardless of the dollar amount of the purchase. Imposing minimum or maximum purchase amounts is a violation.
No Surcharging
Always treat Visa transactions like any other transaction; that is, you may not impose any surcharge on a Visa transaction. You may, however, offer a discount for cash transactions, provided that the offer is clearly disclosed to customers and the cash price is presented as a discount from the standard price charged for all other forms of payment.
Taxes
Include any required taxes in the total transaction amount. Do not collect taxes separately in cash. This policy reflects the needs of the many Visa cardholders who must have written records of the taxes they pay for goods and services.
Split Sales
Prepare one sales receipt per transaction, using the full transaction amount. Merchants are not allowed to split the cost of a single transaction between two or more sales receipts, using a single cardholder account, in order to avoid authorization limits.
Laundering
Deposit transactions only for your own business. Depositing transactions for a business that does not have a valid merchant agreement is called laundering or factoring. Laundering is not allowed; it is a form of fraud associated with high chargeback rates and the potential for forcing merchants out of business.
Zero-Percent Tip
For restaurant transactions with a Visa credit or debit card, authorize only for the known amount, not the transaction amount plus estimated tip. Cardholders now have the ability to check their credit or checking accounts almost instantaneously via phone, the Internet, or an ATM. Consequently, an authorization that includes an estimated tip can reduce a cardholder?s available funds or credit by an unrecognizable or unexpected amount. This kind of transaction may occur if a cardholder leaves a cash tip or adds a tip that is less than the estimated amount used for authorization; for example, if the restaurant authorizes for an estimated 20 percent tip, but the customer adds on only 15 percent.
No Cash Refunds
Complete a Visa credit receipt for merchandise returns or adjustments. Do not provide cash refunds for returned merchandise originally purchased with a Visa card. Visa does not permit cash refunds for any credit or debit card transaction. By issuing credits, you protect your customers from individuals who might fraudulently make a purchase on their Visa account and then return the merchandise for cash.
Colored emphasis mine. They very clearly specify restaurant transactions. Pre-authorizations at a gas pumps and hotels, etc., are considered another matter, and are allowed. Logic would suggest that a gas pre-authorization is for an as yet undetermined purchase, whereas in a restaurant the purchase price has been determined. In a technical sense, a tip is a separate and distinct gift and not part of the meal or purchase, and is only added as a convenience. It is also, technically, a matter between the wait staff and the customer, not the business.