There are some 48,000 barrels of Scotch whisky quietly aging in Martin Armstrong’s warehouses in southwestern Scotland. Last year, 17 of them became a problem.

Mr. Armstrong normally deals with companies that buy hundreds of barrels at a time from distilleries, then pay him to store them as they age. In July, he started getting desperate calls from people who had bought just one or two barrels from an investment outfit called Cask Whisky Limited. They had been told that some of those barrels were stored in Mr. Armstrong’s warehouse.

Cask Whisky had promised those investors sky-high returns. But when the company collapsed last year, it left them scrambling to find their barrels.

“We were inundated by questions,” Mr. Armstrong said.

He couldn’t help most of them. He had never even done business with Cask Whisky. Still, Mr. Armstrong knew exactly what he was dealing with: yet another in a growing number of Scotch whisky-investment scams.

Barrel-investment scams have taken off in recent years, Mr. Armstrong said, because the rapid rise in the price of luxury whisky makes investors willing to overlook red flags.Credit…Emily Macinnes for The New York Times

There are dozens of companies like Cask Whisky, often located in London but selling barrels stored in remote corners of Scotland and Ireland, making it hard for clients to see their investments in person. Some are semi-legitimate operations that sell barrels at prices so inflated they will take decades to turn a profit; others are practicing outright fraud.