Over a cup of tea at the Hyatt Regency London’s Churchill Bar, Sun recalls a particularly challenging mission in 2015.

He was on holiday in Patagonia, Argentina, when he got a request for a £500,000 (US$656,000) watch.

Hong Kong-based Korean bag designer Grace Lee looks to Anya Hindmarch for inspiration

“So from Patagonia, I had to go to Buenos Aires, then to Brazil, and then back to London because the watch was in London,” he explains.

“Then I took the watch to Hong Kong (tax free), and from there to China where I dropped it off. By the time I landed back in London, the client said ‘I’m happy, I want to buy a ring as well.’ So I did the same trip again: London, Hong Kong, Shanghai and back.

“This time when I arrived back in London, he said ‘I want earrings!’ So within one month, I did that trip three times for the same client.”

Sun laughs. He seems aware his problems are not the problems of the average 30-year-old.

Born in Shandong province in eastern China to a modest family, Sun moved to central England to study at the University of Warwick in 2009. (“Business management – boring. I didn’t like it, I’m not a good student.”)

After graduating, he made his way to London and got his first job at a jewellers on Bond Street.

“I never imagined I would be a sales person, but I really enjoyed it. My manager was my mentor and she said, ‘You are a natural sales person … you are selling yourself instead of selling the product’.”

Then followed a short stint in private banking, which Sun curtailed after eight months as he was miserable. “So I started my own business. I approached my previous clients from the jewellers and then gradually built up.”

China’s professional shoppers face renewed scrutiny as government cracks down on agents purchasing goods overseas

Today, the majority of his clients are in Hong Kong.

“I would rather do business in Hong Kong compared with China now, because all my clients moved to Hong Kong or they have a Hong Kong address,” reasons Sun. “For me it’s much easier. I don’t want to fly to China because of the customs issue.”

The Chinese government’s tighter customs controls have made it increasingly difficult for services such as Sun’s, but he’s not deterred. What’s more, he suspects that China’s anti-corruption measures have only managed to target the small fry.

“In the beginning, I had lots of people come to me for transactions under £10,000 or under £5,000,” reveals Sun. “Then, I gradually found all these clients cut off so I was only left with the top few clients. The top clients spend at least £1 million or £2 million per year with me.”

The Brexit vote in Britain hasn’t impacted Sun’s business because, as he puts it, “the super rich always have money for shopping”. And if they’re shopping with Sun, then they’re spending enough to justify his one-on-one time.

“Bond Street and Harrods are my favourite. I have access to Harrods’ top private suite, which is for VIP clients such as politicians or royalty. You can’t find the door, it’s very discreet.”

Sun talks about shopping with the same fervour as he does travel, fine art, and horse riding. He can’t bear to buy leather goods from anyone besides Hermès or Goyard, because “after you’re used to the quality, you can’t say yes to a Louis Vuitton or a Bottega Veneta”. But he’s given up trying to influence his clients, whose tastes run more towards Chanel.

“What they value is getting what they want … and the discount,” says Sun. “They bargain with me, and then I bargain with the brands.”

But since Chanel launched its global harmonised pricing strategy, the price difference between China and the UK is negligible.

“Watches are cheaper here, for sure,” declares Sun, who doesn’t deal with fashion unless specifically asked to by clients. Asked which brands are currently in vogue, Sun is blunt.

China’s luxury goods market begins recovery as middle-class shoppers eye bargains at home

“Rolex, Patek Philippe … Rolex less and less because Rolex is cheaper than other brands. Richard Mille, the price is ridiculous. Hublot is rubbish now, nobody buys Hublot. Jaeger-LeCoultre, no, because the entry-level price could be £3,000 – with Richard Mille, the entry-level price is £75,000. It’s a different level.

“The super rich either don’t want other people wearing the same brands as them, or they want to wear the same brands as their friends.”

So could Sun ever see himself moving back to China, or perhaps to Hong Kong?

“I couldn’t,” replies Sun, dismissing the idea out of hand. He pauses to take a sip of his chamomile tea before adding: “If you’re a millionaire, you can have a really good lifestyle in London. But in Hong Kong, you have to be a multibillionaire to have a good lifestyle there. For sure.”