So this motability customer has to do all the running because motability did not inform DVLA that they had sold the car. This happens every day in life with motability they just don’t do a simple job on a computer to tell someone that the car is no longer there’s. And if he contacted DVLA a couple of days later you can be assured it will be out of his name then ok.
I agree that Motability have messed up, but the harsh reality is that until the change has been made the previous driver will be the one who gets any fines and is accountable for them until such time as they can prove that they no longer had the vehicle at the time. These things can be easily resolved by doing as I suggested, which @Retro89 has now done.
The solution that you proposed of just ignoring it is not sensible for a multitude of reasons. Fines have a habit of escalating if not paid quickly. Police issued fines will progress to Magistrates if not paid and then you incur court costs and potentially bigger fines as well. Many other fines are civil matters and the escalation levels can involve debt recovery agencies. Nobody in their right mind wants to have all that worry hanging over them, or the hassle of having to get things overturned once they’ve been escalated, especially when a quick call to Motability and sending the proof that you weren’t responsible for the car at the time gets it resolved very quickly without any of that hassle.