A party of four walks into a Michelin-starred restaurant with eight trophy bottles of ultra-high end cabernet—each worth over $1,000—and they're hinting at having their corkage fees waived.

Suddenly, the sommelier is enmeshed in a game of high-stakes diplomacy requiring the art of a United Nations sidebar. The goal: keep big-shot wine collectors happy without losing too much money on the table.

"They say, 'Oh, we didn't realize there was a limit,' and, 'Come on, what's the big deal? These are very special bottles,'" one noted sommelier lamented. "It becomes a guilt trip."

Succumbing to the pressure, in this case, demands 32 hand-buffed glasses, five decanters, and "one human being's entire night" to service an hours-long dinner. It saps the restaurant's resources and could cost more than is made on the tab, because beverage is most restaurants' profit-driver and this four-top will have none. "We have to sell wine, and if we don't sell wine, we don't exist," said the sommelier.

In speaking to wine professionals—all from top Manhattan restaurants and all of whom only spoke under the condition of anonymity to avoid offending patrons—it is clear that begging out of corkage fees is a too-common practice among New York's wealthy diners. Some have even coined a term for them: corkage cowboys.

Collectors will often offer a taste of their trophy wine to the sommelier. Most view it as a gracious perk; not a quid pro quo, which is how the cowboys employ it.

One sommelier said the cowboys were generally "mid-career finance guys"— bankers, hedge funders, and money managers who surface at restaurants about once a month. "They swim in the same circles. They all know each other, go out together, and have the same perspective." Playing one restaurant off another, he said, "They collectively boycott those that don't conform. It becomes a pack mentality."

Most guests do happily abide by corkage policies. But cowboys work the gray areas, forcing sommeliers to do an uncomfortable table-side calculus on behalf of their restaurant's owners.

One move cowboys use to evade corkage fees is a twist on a common gesture of goodwill. Collectors will often offer a taste of their trophy wine to the sommelier. Most view it as a gracious perk; not a quid pro quo, which is how the cowboys employ it.

"I've seen it in every single restaurant," says one noted sommelier. "They think we're going to geek out. Like, 'Oh, yeah, Screaming Eagle, great.'" And it would be great, except that the nicety is manipulated. "Once a staff member begins drinking from that bottle, the assumption is that the corkage fee will be waived." said another top wine professional. "That's not a gift of generosity; it's a gift of expectation."

Some restaurateurs try to deter cowboy-like behavior by setting their fees astronomically high ($150 per bottle at Per Se, for example) and prohibiting bottles that can be found on the restaurant's wine list.

Places like Daniel, Del Posto, and Le Bernardin simply don't allow customers to bring their own wine. These are zero-tolerance policies: "You could be the President and you cannot bring wine into my restaurant," said one no-corkage sommelier. Sorry, Obama, but you'll have to leave that 1976 Domaine de la Romanée-Conti at home.

To some, it seems strange to BYO to the planet's finest dining establishments. "You wouldn't bring food, would you?" said one beverage director. "Like, walk in with a pizza and say, 'Send a slice back to the chef.'"

'We're arguing about a $40 or $50 corkage fee, but we're talking about bottles that are thousands of dollars!'

But there are times when sommeliers encourage their diners to arrive with their own wine. "Someone went to an estate on their honeymoon," says one, "or the vintage is the year of the birth of their first child ... it becomes an allegory of their relationship—that brings a tear to my eye."

According to another sommelier, however, those occasions are "super-rare" and, most of the time, customers "want to drink fancy wine with their meals but don't want to pay as much for it." Setting corkage policies that don't toss the baby with the Bordeaux bathwater is a nimble dance. Says one wine pro, "You always hear horror stories: You give an inch, and they take a yard, bringing bottle after bottle."

The cowboy phenomenon appears to be special to New York. In San Francisco, in contrast, the corkage dynamic is way more chill. "People understand you have to charge something—I mean I have five sommeliers," said Mark Bright, wine director at Saison, a three-Michelin-starred restaurant. Diners generally don't have a problem paying corkage there.

The perplexing question remains: Why do these wealthy diners haggle? As one frustrated sommelier put it, "We're arguing about a $40 or $50 corkage fee, but we're talking about bottles that are thousands of dollars!"