In Vino Veritas. In Napa, Deceit.

When you buy a bottle of Napa Valley cabernet sauvignon, you trust that the bottle is filled with wine actually made from cabernet sauvignon grapes that were grown in the heart of California’s wine country.

The strange tale of Jeffry James Hill might make you question that faith.

Mr. Hill, 36, was a longtime Napa vineyard manager who worked his way up from agricultural pest control to stake a claim as a maker of $100 wines.

In 2012, he set himself up beside some of the most prestigious names in the business when he leased a winery along Napa’s Silverado Trail, a destination for wine aficionados from around the world.

A beefy man with the bearing of someone accustomed to working the land, he could hold a busload of tourists spellbound with homespun stories of a vintner’s life. Mr. Hill also had a knack for marketing, getting Hill Wine Company bottles on the United Airlines planes shuttling American athletes to the Winter Olympics in Sochi, Russia.

At the same time, he continued to work in the less glamorous side of the industry, buying and selling grapes and bulk wine and managing fields for big wineries and small growers. His commercial clients included famous names like Don Sebastiani & Sons, Del Dotto Vineyards and Trinitas Cellars.

It was all built on quicksand. The fancy winery was more than Mr. Hill could afford, and the expenses of operating the business quickly outpaced his income. He was soon deeply in debt and resorting to deceptions like substituting cheaper merlot and malbec grapes for the much more expensive Napa cabernet sauvignon advertised on the wine labels, according to court documents. Prosecutors say he even engaged in outright theft.

Mr. Hill worked in an industry built on romance, expensive land, hard labor and a whole lot of faith, and the accusations against him have shaken the wine-growing region.

“The system is only as good as how trustworthy people are,” said Ned Hill, who is not related to Jeff Hill, and who farms for several major wineries in Sonoma County through his company La Prenda Vineyards Management.

The federal government forced Mr. Hill to cede control of his business on April 23, and Napa County prosecutors have charged him with two felonies, saying that on two occasions in October 2013 he stole grapes that his crew was harvesting for another winemaker and diverted them to his own winery.

This month, he pleaded not guilty to the criminal charges, and a trial is set to begin April 13. If convicted, he faces up to four years and eight months in prison.

Hill Wine has filed for bankruptcy and owes more than $8 million to creditors.

“In the wine business, there’s always been some level of this,” said Rob McMillan, executive vice president and founder of Silicon Valley Bank’s wine division.

In September, Italian police seized the equivalent of 220,000 bottles of cheap wine that was accompanied by false documentation that claimed it was premium wine from Montalcino, home of the renowned Brunello wines. Police estimated the cache would have had a retail value of about 5 million euros, or $6.5 million at the time of the bust. A month earlier, a New York judge sentenced Rudy Kurniawan, a Southern California wine collector and seller, to 10 years in prison and ordered him to pay $28.4 million in restitution and forfeit $20 million in property. According to the court, he had for years carried out an elaborate fraud in which he blended lesser wines to mimic rare vintages, put them in old bottles, pasted false labels on them, and sold them to wealthy buyers.

Even Fred Franzia, chief executive of Bronco Wine, the company that makes what is known as Two-Buck Chuck, was once caught mislabeling grapes. After he pleaded guilty to conspiracy to commit fraud in 1994, he and his company paid $3 million in fines.

The Jeff Hill case has reminded the California wine industry of the risks of deception, said Ned Hill, the Sonoma vineyard manager. “Everybody is a lot more careful now about asking questions,” he said. “It’s made people dot their Is and cross their Ts.”

Given the scale of Mr. Hill’s purported fraud, those hurt by his actions are wondering why federal authorities have not brought any charges against him or the winery. Bryan Tong, the Napa County prosecutor handling the Del Dotto theft charges, said he had had no contact with federal authorities. Still, liquor regulators are keeping a close eye on the wines touched by Mr. Hill.

When Mr. Westfall of Invino, the online wine retailer, bought thousands of bottles of Hill Wine’s pinot noirs and cabernet sauvignons for $5 each at a bankruptcy auction in September, one of the T.T.B. agents on the case quickly contacted him, he said.

She told him that three of the cabernet bottlings, claiming to contain grapes from the Stags Leap, Coombsville and Atlas Peak areas of Napa County, were mislabeled and could not legally be sold in the United States without changes. Mr. Westfall said he sold about 1,800 of the questionable bottles overseas, but is still searching for buyers for 7,200 bottles.

The T.T.B. raised no objections about the rest of the wines that he had won, including the high-end 2011 Jeff Hill cabernet that my wife and I enjoyed so much that day we visited the winery.

Invino now sells that wine for $30, down from its original list price of $96. In his write-up of the cabernet online, Mr. Westfall calls it a “home run” and says, “Our panel had the pleasure of tasting through these wines and we can tell you with absolute certainty that this is by FAR the best deal we have ever been able to secure.”

Explaining his exuberance, he recently poured me a taste. It was just as lush and rich as I remembered — and at $30, it was enough of a deal that I bought four more bottles.

“What is something worth?” Mr. Westfall said. “Whatever people will pay for it.”

A version of this article appears in print on January 25, 2015, on page BU1 of the New York edition with the headline: In Vino Veritas. In Napa, Deceit.. Order Reprints| Today’s Paper|Subscribe

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