(FORTUNE Small Business) – At an independent hotel South of San Francisco, lunch is being served outdoors today for the first time this spring, but the guest dining with me is not happy. The woman--Dallas-born, thirtysomething, call her Madame Inspector--says, "The waitress should never bring a dirty dish to greet a new table." Then she adds, "Look--at--that!" indicating a busboy squeezing between my chair and an ochre-colored pillar. She orders just one course from the prix fixe menu, hold the potatoes, please. The harried waitress double-checks to find out if that order is allowed, then departs, earning another frown. "The waitress shouldn't have to shout to ask her boss if a change in the menu is okay," Madame I says. "It should never be a problem."

This is the busy season for Madame I, who inspects hotels, usually anonymously, for Small Luxury Hotels of the World, a consortium of more than 300 upscale, independently owned properties in 50 countries (including 44 in the U.S.). The hotels apply to join SLH, but before being accepted, they get checked out by Madame I or one of five other inspectors. The annual SLH roster is finalized each July, so the months before are a flurry of surprise visits and other research. Last year SLH accepted just 44 of 194 applicants. In addition to being independently owned and small for their market--most have fewer than 100 rooms; the average is 64--the hotels must meet certain standards of luxury, which Madame I ensures by her 24-hour inspections. (For more on how independent hotel associations work, please see "Inn Crowd.")

Madame I has a degree in restaurant and hospitality management and worked for an upscale Dallas hotel chain before she joined SLH ten years ago. Not all of her trips are as easy and luxurious as you might guess. She has been chewed by sand flies in St. Croix, had vervet monkeys steal her breakfast at the Ngala Private Game Reserve in South Africa, and suffered enough allergy attacks and stomach aches that her carryon bag now looks like a traveling pharmacy.

At the California hotel (which she asks us not to name), Madame I leaves lunch underwhelmed but says the manager warned her that this hotel needed work. When the owners applied for SLH membership, the manager, who had taken over only recently, said he wanted a month or two to make improvements before an inspection. Though she plans to make another visit after those changes, Madame I decided to stop by without warning so she wouldn't get special treatment. (That happens--once, while she was inspecting Hotel Hana Maui after the island's heaviest-ever rainfall, the entire village helped hose the mud off the gardens before her arrival, and the staff posed as guests to make the dining room seem full.)

After the service glitches at lunch, the hotel's décor wins back major points. The lobby has lots of burgundies and chocolate browns, in the style of southern Spain. The rooms turn out to be even better. "I love it," Madame I says, pushing open a varnished wooden door to reveal custom furniture, a pomegranate-colored satin duvet, hand-painted pottery, two TVs and DVD players, and a double-sided gas fireplace. "Masculine but unintimidating," she concludes. "I prefer an airy style, but this is like foie gras: I don't like it myself, but I can tell if it's well presented."

She pulls open the drapes, turns on the AC (to time how quickly it cools the room), and gets to work. Opening the minibar, she checks the expiration dates, knowing that some items can sit untouched for years. She picks up the phone (cordless, a plus), looks for any makeup smudges left by previous guests, and calls room service. "I always count the number of rings, and I expect them to call me by my surname," she says. She counts the hangers in the closet and checks for customized dry-cleaning tickets. Leaning into an air vent, she takes a big sniff.

Many of Madame I's best insights come from checking out the off-limit areas most guests never see. She often pretends to "accidentally" wander into accounting offices and kitchens. She also talks to the staff--especially people who don't normally deal with guests. By this measure the hotel does well. A housekeeper boasts that she mops the lobby floor three times a day, and a gardener chats about the grounds. Madame I says she is repeatedly surprised by staffers. At one hotel in the Bahamas, years ago, she asked a pool waiter whether jerk chicken was on the menu. "He said it wasn't, but the next day he brought me some," she says. "His mom made it for me."

At dinner, the hotel continues to redeem itself. The service is friendly and perfectly timed, even though Madame I is pulling out all her tough questions. She orders one appetizer for two to see if they'll split it onto two plates, and she asks for veal scaloppine, but made with chicken. No problem. A final sneaky trick--she uses her entrée fork for her appetizer and watches as they replace it.

In the morning Madame I reveals herself to the hotel manager. He is surprised at her visit but eager to hear her feedback. The grounds are impeccable, she tells him, and the rooms pristine. Before she can get into the service problems at lunch, he anticipates her. "Service is inconsistent because the restaurant was managed separately until a month ago," he says. "This is what I'm working on. It'll be fixed in a month or two." Madame I tells him, "With those changes, I'll recommend you with pleasure." As of presstime, the hotel was reviewing its restaurant staff, and she was planning a return trip.

In July, when the 2004 SLH list is done, Madame I will finally get some time at home. But she has exacting standards there too. "You can bet every toilet paper roll is folded into that famous triangle," she says.