BEVERLY HILLS, Calif. — “ It started with a clip of a car pulling out,” RD Whittington said from the head of a table in a private dining room at Mastro’s Steakhouse. Mr. Whittington, a car dealer, was wearing a black T-shirt, chain necklace and sparkly Audemars Piguet watch. He was sitting across from Jamie Foxx, whom he calls his best friend and business partner.

That car, a rare, six-wheeled Mercedes-Benz G63 AMG 6x6, was the first sale Mr. Whittington made through his Instagram account, @wiresonly. “A DM comes in and goes, ‘Hey, is that car for sale?’” he recalled. “‘Yeah,’ I said. He said, ‘Send me some pictures of the inside.’ And then he’s like, ‘I want it. I’ll take it.’”

A partner in the Luxury Auto Collection of Scottsdale, Ariz., he has moved millions more dollars worth of metal through his Instagram account, which has, since it was started in 2015, become the go-to place for celebrities and C.E.O.s with the faith to make a wire transfer on the spot. Exotic cars (expensive, high-horsepower cars typically imported from Europe in limited quantities) are his specialty.