The story of John Carmack being barred from buying a Ferrari after tuning some of his own is a bit more nuanced than the question suggests. While Ferrari didn't explicitly ban Carmack from purchasing their cars, his modifications to Ferrari vehicles did cause some controversy.
John Carmack, the co-founder of id Software and a well-known programmer, is also a car enthusiast. He owned several Ferraris and was known for modifying them, particularly by adding turbochargers to increase their performance. This practice goes against Ferrari's philosophy and their strict control over their brand and products.
Ferrari has a history of being protective of their cars' designs and performance. They often include clauses in their sales contracts that restrict certain modifications or require approval for changes. The company believes that their cars are engineered to perfection and that unauthorized modifications could compromise their performance, safety, and brand image.
Carmack's modifications, especially adding turbochargers to his Ferraris, were seen as particularly sacrilegious in the Ferrari community. While it's not confirmed that he was officially banned from buying new Ferraris, his actions likely strained his relationship with the company.
It's worth noting that Ferrari has been known to be selective about who they sell their limited-edition models to, often favoring long-time customers who respect the brand's values. Carmack's modifications might have put him at odds with these values, potentially affecting his ability to purchase certain Ferrari models in the future.
The incident highlights the tension between car manufacturers' desire to control their products and enthusiasts' wish to personalize their vehicles. While many car companies embrace aftermarket modifications, luxury brands like Ferrari often have stricter policies to maintain their exclusivity and brand integrity.