When Donald J. Trump appeared at Sneaker Con in Philadelphia last weekend to promote a limited-edition line of gilded high-tops, there were a lot of boos in the crowd, but none coming from Roman Sharf.

A watch dealer who is known for his selection of tangerine-size Audemars Piguets and Patek Philippes, Mr. Sharf ended up buying an autographed pair of the “Never Surrender” sneakers after placing a $9,000 bid through an auction held that day over the app Whatnot.

“They’re still new — they smell like glue,” Mr. Sharf said Friday morning as he held the shoes to his face and took a whiff.

Above each ankle was an American flag of sorts, comprising red and black lines and a blue box filled with spangly stars and stripes. There were Ts embossed on the tongue and Ts on the sides. The former president’s signature appeared in thick black ink on the shiny right toe box.

As he showed off his prize, Mr. Sharf was standing on the second floor of the small building in Southampton, Pa., that is the headquarters of his company, Luxury Bazaar. Except for the shell of a 2019 Formula One car that serves as a kind of sculpture, the space looked like a vault.

Behind him was an office filled with vintage Louis Vuitton trunks, old cassette tapes by Jay-Z, Whitney Houston and 2 Live Crew, among others, and an orange Pelican case containing two dozen timepieces that he said were collectively worth around $3 million.

Mr. Sharf was wearing blue Nike X Sacai “Fragments,” faded Dsquared jeans and a navy blue golf jacket that he had bought on Wednesday on a visit to the Trump International Golf Club in West Palm Beach, Fla.

He had wound up at the club because he had proudly posted about his Sneaker Con acquisition on his social media channels, where he has hundreds of thousands of followers. Afterward, Mr. Trump extended a lunch invitation. So Mr. Sharf jumped on a plane and headed to the golf club with his 20-year-old son, Marcus Sharf, who lives in Miami and runs a high-end sneaker and streetwear boutique, HYPMiami.

Mr. Sharf had the Caesar salad and chicken noodle soup. Mr. Trump munched on his trademark burger and fries. After the lunch, Mr. Sharf’s rabbi texted to ask if they had discussed the situation in Israel, but no such luck.

“It was like talking with friends,” Mr. Sharf said. “It was a normal conversation, no agenda.”

A fair number of Mr. Sharf’s several hundred thousand followers on YouTube, Instagram and TikTok had a different reaction: They said they were going to unsubscribe to his feeds as a result of his support for Mr. Trump. Some of the online anger was stirred up by an article in The Daily Mail about Mr. Sharf’s sneaker purchase that described him as a “Russian oligarch” who was prone to “MAGA mania.”

Mr. Sharf professed not to be bothered by the criticism. “I’m on social media,” he said. “I’m used to haters.”

He added that he was in the business of catering to people with money — and many of those people are Republicans who were happy to see him profess his allegiance to Mr. Trump. But Mr. Sharf did have a few things he wanted to clear up, including that he is not Russian, but Ukrainian.

He said he was 13 when he came to the United States with his stepmother, his older sister and his father in 1988, three years before Ukraine broke away from the Soviet Union and became an independent nation.

“He had $4 in his pocket,” Mr. Sharf said of his father.

The family moved to Sheepshead Bay, Brooklyn, and lived in a tiny apartment in one of the buildings operated by Fred Trump. His father found employment at a company that welded canopies at stores and worked as a waiter on weekends. His stepmother was an accountant.

After high school, from 1993 to 1996, Mr. Sharf served in the U.S. Army. He was stationed in Camp Pelham, South Korea, then moved to Fort Knox in Kentucky, records show.

From there, he put in two years at Pennsylvania State University before heading to the Philadelphia area, where he attended a trade school for computer programming. He then took a job at HealthPartners Inc., an insurance provider. When his annual salary passed $50,000, he had enough to pretend at having wealth.

“I leased a BMW 3 Series and got a Rolex Datejust for $1,000,” he said. “It walked into the room before I did.”

Mr. Sharf held out his arm, displaying how he used to flaunt his Rolex. The timepiece now dangling from his wrist was a vintage yellow gold Patek Philippe Nautilus sports watch that trades for 200 times that much, give or take.

By the late 1990s, he was at Deutsche Bank, working in infrastructure support. On the side, he began selling watches on eBay. His sideline took off, and in 2006, he founded Luxury Bazaar. It now has 30 employees and two offices — one in Southampton, Pa., the other in Hong Kong. He lives with his wife, Anna Sharf, and their two younger children in a suburb of Philadelphia.

Mr. Sharf said he was decidedly opposed to Russia’s invasion of Ukraine. “I don’t even understand his goal,” he said of President Vladimir V. Putin. He added that, in his view, Mr. Trump would be the “one president” who could bring the war to an end by sitting the two sides down and hammering out a deal.

“I’m a strong proponent of the First Amendment and the right to bear arms,” Mr. Sharf said. “I also believe in gay marriage and the right to abortion. Within limits.”

“Everybody to me is green,” he continued, invoking a saying from his Army days. “That’s what the military teaches you, because we all wear the same color uniform. What I hate to see is division. We’re one people under one flag.”

Although his shoes had two. One for each foot.