Groucho Marx would have quipped that investors should never buy a stock someone else is trying to sell. This is especially true when families put their businesses on the block.

Four months ago, Sweden’s Wallenberg family sold VW its 31 per cent block of voting shares in truck producer Scania. The German carmaker paid SKr200 per share – equivalent to a torquey 18 times next year’s earnings. With Scania now trading at SKr84, the Wallenbergs timed their exit to perfection. The share prices of compatriot Volvo and Germany’s MAN, also 29 per cent owned by VW, have also hit the skids in recent months.