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.