Donald Trump was booed during a surprise appearance to unveil a new line of $399 trainers on Saturday – a day after he was fined $355 million for fraud.

The crowd at the Sneaker Con in Philadelphia jeered at the former president as he launched his “Never Surrender high-tops”, using the platform as another campaign stop between court and primary elections.

Holding his golden trainers, Mr Trump said “wow, there’s a lot of emotion” as he responded to the crowd, some of whom were also cheering.

The trainers, with an American flag detail on the back, are being sold for $399 on a new website that also sells other Trump-branded shoes and “Victory47” cologne and perfume for $99 a bottle.

A standard style trainer is also offered in either “T-Red” or “POTUS” white, both with a golden “45”, representing Mr Trump’s time as the 45th president, on the side. The slip-ons sell for $199.

“This is something that I’ve been talking about for 12 years, 13 years. And I think it’s going to be a big success,” he said.

The trainers are one in a string of money-making ventures Mr Trump has embarked on since launching his third campaign for the White House in 2022.

Last year he reported making between $100,000 and $1 million from a series of digital trading cards that portrayed him in a series of cartoon-like images, including as an astronaut, a cowboy and a superhero. He has also released books featuring photos of his time in office and letters written to him through the years.

Before running for office, Mr Trump sold everything from steaks to vodka to a venture he called “Trump University”.

Mr Trump revealed his new trainer line just a day after a New York judge ruled he must pay $354.9 million in penalties for fraudulently overstating his net worth to dupe lenders. Judge Arthur Engoron also banned him from serving as a company director or taking out loans from banks in New York for three years.

The judge said of Mr Trump and his co-defendants: “Their complete lack of contrition and remorse borders on pathological.”

The fine came on the back of another, in which Mr Trump was ordered to pay an additional $83.3 million to the writer E. Jean Carroll for damaging her reputation after she accused him of sexual assault. With interest payments, Mr Trump’s legal debts might now exceed a half-billion dollars — an amount it is unclear he can afford to pay.

Mr Trump hit back at Mr Engoron on Saturday, saying the decision was an “election interference plot” and accusing the judge of being part of a “Left-wing” conspiracy aimed at preventing him from becoming president again.

“A crooked New York state judge just ruled that I have to pay a fine of $355 million for having built a perfect company,” the former president said from Mar-a-Lago on Friday. “It’s a witch hunt against his political opponent, the likes of which our country has never seen before.”

Mr Trump also faces four state and federal criminal trials, including one scheduled to start in New York on March 25, over alleged hush money payments to a porn star. Mr Trump will become the first former US president to stand trial on criminal charges.

Attendees of the Sneaker Con event were younger and more diverse than Mr Trump’s usual rally crowds, according to the Associated Press. The presidential hopeful’s team is hoping he will be able to win over more young and minority voters in a likely rematch against Joe Biden in November.