The suspect had expressed interest in buying a 1985 Ferrari 288 GTO, police in the German city of Düsseldorf say.
He turned up by taxi to the dealership and two hours later, on a test drive, it was time to swap drivers.
But when the seller stepped out of the car, the would-be buyer quickly hit the accelerator and vanished. The car was later found in a garage.
Police say the "historic vehicle" with 43,000km (27,000 miles) on the clock should be valued at more than €2m.
A listing for the car on the dealer's website says it once belonged to former Northern Ireland Formula 1 driver Eddie Irvine – who raced for Ferrari between 1996 and 1999.
Similar vehicles are frequently listed with prices around £1.5–2m, or above $3m in the US. They are often sold through specialist auctions at the likes of Sotheby's.
Luckily for investigators, the distinctive car - in bright Italian "Rosso Corsa" red - attracted so much attention that it was quickly found on Tuesday evening after police appealed for witnesses.
It was discovered hidden in a garage in the town of Grevenbroich, not far from Düsseldorf city centre.
The suspect, however, remains at large. Police have released a photograph of the man inspecting the Ferrari before the theft.
The managing director of the dealership told Westdeutsche Allgemeine Zeitung newspaper the man had exchanged calls and emails over the course of a number of weeks.
Bernhard Kerklo told the newspaper the car could never be sold on the market as it was "too flashy".
Insiders - the only real buyers for such a rare collector's item - would instantly know it was the stolen vehicle, he said, as all the models of this type ever sold are well-known.
Only 272 of the Ferrari 288 GTO were ever built.
BBC
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