If the growth trend remains positive - sales triple in ten years, from $11 billion to $30 billion - profitability is going through a serious air pocket, since net income is back to its 2013-2014 levels.

The reasons for this are: a drop in like-for-like sales, linked among other things to the emergence of new players such as Carvana; the rise in interest rates, which restricts credit activities and leads to a first series of payment defaults; and the cost of investments in the digital transition, among other things.

The most glaring weakness of CarMax's business model remains the lack of operating leverage. This can be seen in the margin compression that accompanies the spectacular sales growth.

On a more positive note, the U.S. used car market is huge, with nearly 40 million units sold annually. It is also still very fragmented, and largely dominated by CarMax, which sells three times as many vehicles as its leading competitor.

By 2026, the group intends to sell 2 million vehicles a year and generate $33 billion in revenues: as we can see, there should be no shortage of opportunities for consolidation, even if in the past CarMax has grown mainly organically.

It is worth noting that the management has been very successful in breaking into the wholesale business. This segment now represents a quarter of the turnover, and ensures a competitive supply cost on the retail segment.

In reality, the current concern is of course the credit segment. CarMax lends directly to its Tier 1, so-called prime, customers and subcontracts almost all of the loans to Tier 2 or 3, so-called subprime, customers; but the whole thing remains a black box, and the creditworthiness of the borrowers is questionable.

The history of profitability of the credit activities is good, but it is not clear whether this trend will be sustainable in the new interest rate environment. This context is weighing on all the players in the sector - for example, Ally Financial, which has since become a new position of Berkshire Hathaway.

By the way, CarMax is pursuing a capital allocation strategy dear to Berkshire, since the group has redirected four-fifths of its profits from the last decade to share buybacks.

If the group manages to return to its historical profitability levels, it should be able to generate between $1.2 and $1.5 billion in profit per year. It is difficult to resist the current valuation if you subscribe to this scenario.

However, we will have to deal with the great opacity of the business model.