LAS VEGAS — In the rarified world of luxury hotels, it's not only the thread count of the sheets or the sheen of the marble but the sincerity of the staff that separates the best from the rest.

Casino developer Steve Wynn recalls getting the bad news that his Bellagio resort would be getting four stars instead of five from Mobil inspectors more than a year after its opening in 1998.

"It was an unfortunate exchange at the front desk with the anonymous shopper," said Wynn of the property now owned by MGM Mirage Inc. "And room service trays, after people had eaten breakfast, were left outside the door in the hallway."

While such minor annoyances might have been acceptable in the land of free drinks, bargain buffets and sequined showgirls, such service no longer passes muster in upscale Sin City.

As budget options like the Stardust and New Frontier have been imploded to make way for more expensive, classier resorts, a battle is being waged for the tourist dollars of the upper crust.

Details such as pronouncing a hotel guest's name correctly and delivering room service within five minutes of the appointed time are crucial to attaining the top ranks from such agencies as Mobil, AAA and Michelin.

Higher rankings mean higher room rates for operators. Likewise, restaurateurs covet the rankings, which bring headlines and crowds of big-spending customers.

RATINGS MEAN MONEY

In the case of The Venetian, owner Las Vegas Sands Corp. was able to raise the average daily room rate in the first three quarters of 2007 by $22 from a year earlier — to $259 — after spending $100 million on renovations to achieve five-diamond status from AAA.

For the 4,000-room hotel, which opened in 1999, that means millions of dollars more to the bottom line, said senior vice president Paul Pusateri, who spearheaded the drive to improve its four-star rating.

The property doubled the number of pillows on each bed to four, increased the thread count to 260 on its sheets in standard rooms and installed flat panel TVs and automatic drapes.

It also began running secret shoppers through its property at least every two weeks, testing employees on hundreds of AAA and Mobil rating criteria, such as making eye contact, dealing with communication breakdowns and responding to requests quickly.

When service slips, employees are notified immediately.

"It is as simple as one team member not being able to pronounce the name of the shopper and therefore not using it, for example," hotel operations vice president Kirsten Dimond said.

At the Wynn Las Vegas, whose Tower Suites hotel-within-a-hotel was awarded Las Vegas' only Mobil five-star resort rating last year, average room rates were a market-leading $282.

"Rich people know what the best hotel is in every city of the world," Wynn said. "Mobil is a confirmation of that."

Celebrated chef Joel Robuchon, whose namesake restaurant at MGM Grand received Michelin's only top three-star rating in Nevada last month, said the key is guest satisfaction.

"I'm very happy about it, but the stars are not my main focus," Robuchon said by telephone from his restaurant in Macau. "For me, the best thing that can happen is when guests make their next reservation even as they are leaving."

The Las Vegas area boasts five resorts and four restaurants with five diamonds and more than a dozen of each with four. Elsewhere in Nevada, there are five AAA four-diamond properties, including the Hyatt Regency Lake Tahoe Resort, Spa & Casino; Harrah's Lake Tahoe; and Cactus Petes Resort Casino in Jackpot.

Reno's best properties, such as the Grand Sierra Resort & Casino; Eldorado Resort Casino Reno; and Siena Hotel Spa Casino, received three stars and diamonds from Mobil and AAA.

PASSING MUSTER, OR NOT

The key to great hotel service is the arrival sequence, and it begins beneath the covered driveway known as the porte-cochere.

On a recent, unannounced annual inspection, The Associated Press accompanied an AAA inspector into the Hilton Grand Vacation Club on the Las Vegas Strip, most recently ranked as a three-diamond hotel.

The green Subaru wagon arrived on a not-busy Tuesday afternoon and the visitors already were out of the vehicle before three valet workers moved to assist them.

"I see the valets, and they're just sort of chitchatting," said the inspector, who asked not to be identified so she could perform occasional anonymous stays. "This could be a four. Did I get four-diamond service on arrival? No."

Inside a room, assistant executive housekeeper Gerardo Chavez-Mendoza nervously looked on as the inspector ran her hands over the granite countertops and then into the coffee maker, with the drama of a mother inspecting her teenage son's room.

"You're not going to like this," she said, pulling out a wet, used coffee bag.

"Wonderful," Chavez-Mendoza said, visibly upset.

North America's most popular guidebooks — Mobil and AAA — rank up to three levels on their respective star or diamond charts with in-person, unannounced inspections. A rank of four or the highest, five, requires an incognito stay.

As a result, property managers encourage their employees to be on the ball — all the time.

"After the first six months, they really realized there's no point in trying to find out who the shopper is," said the Venetian's Dimond.

Cleanliness, safety and reliability are the base standards for obtaining a listing in the guides and the lowest one star or diamond rating. From there, standards diverge slightly.

A GOOD THING FOR ALL

Mobil requires onsite restaurants for a two, while AAA does not. At a Mobil three, the bathroom is expected to have "hygienic soap, shampoo and four other bath amenities"; while AAA expects "two large bars of soap or equivalent; one bottled item; attractively presented" and other amenities at the front desk.

At the four and five levels, rooms are expected to feature such touches as accent pillows, artistic interiors, insulated ice buckets, bathrobes and often brand-name bath goods. Warm, sincere greetings, often by name, are expected in every interaction.

Some properties attempt to go beyond the requirements, aiming for the wow factor that amazes guests and secret shoppers.

At Bellagio, a five-diamond, four-star property, flowers are shipped in from around the world to fill the 13,500 square-foot conservatory, which is changed out five times a year.

"We go out and search for the Christmas tree that we need three, four months in advance. We fly flowers in from Holland," president Randy Morton said. "That's a Bellagio diamond, I guess you'd call it."

At the highest levels of service, Mobil rates only 37 hotels and 16 restaurants as five-star in North America; while AAA gives its top designation to 100 hotels and 60 restaurants in the U.S., Canada, Mexico and the Caribbean. Michelin, known more as a restaurant guide, gave its top three stars to 68 restaurants in 22 countries, but it's unclear how many hotels got the top honor of five red pavilions.

When Wynn won his coveted Mobil five stars last year, he said he spent millions advertising it, not only to flaunt the distinction, but to egg on his competitors.

"Since I made a fuss about our five stars, that will inspire other people in town to be jealous and to upgrade," Wynn said. "The more that Las Vegas is perceived to be a really high-class destination, the bigger the market gets. That's a good thing for all of us."