It depends on how it's been driven and when it was reset. If it's only ever been to the local shops or has recently been reset and driven around a dealer's forecourt, it's not a problem.

I happen to see a 5 year old Honda CRV deisel for sale. The display showed it as 24mpg.

Would there be something wrong with this car with such bad mpg?

If the system is the same as the Civic which I would have thought it is, if you reset mileage after topping up the fuel tank, the MPG guage reads from zero and works up according to mileage and speed, ie its not bad its starting from scratch or fuel top up.

they can be set to reset mileage and MPG on fill up automatically in settings