“It’s all we’ve got,” said James Barron, who found a buyer for “Mimi,” a 1955 Alice Neel portrait, during the online edition of the Dallas Art Fair in April. It sold at a discount to the $700,000 asking price.

There are limits to buying art sight-unseen. Collectors’ confidence often depends on their familiarity with an artist’s work, the person selling it and the price. Sherman said he was comfortable spending $3,500 to $25,000 per work, including an $18,000 painting by Woody De Othello from Jessica Silverman Gallery.

He bought from the galleries he knew or those he discovered on Platform, a digital initiative by Zwirner to highlight newer galleries in New York, London and Los Angeles.

But seeking fresh talent without the imprimatur of a blue-chip gallery might be tougher.

“I am not looking at any viewing rooms except for the artists I know and follow,” said Alain Servais, a Brussels-based collector.

Baird Allis, a Chicago attorney who collects Old Masters, had been skeptical of buying works online.

“Pictures always look great in the catalog,” he said. “When you see the painting in person, it often doesn’t look the same.”

But then his Sotheby’s contact told him about the online sale of the works amassed by Old Master dealer Rafael Valls. He viewed high-resolution images and received detailed condition reports before bidding on a few lots. He won a small Dutch landscape painted in 1627.

“It’s a charming, little, decorative painting,” Allis said. “I had a nice spot for it in my office, and the final price was under $10,000.”

More expensive works are a different story.