Just on price - is the 290k what he actually paid? Or settlement on it now, so actual price was far less? Is the 190k offered a trade for another car or a dealer buying outright?
I'd say try 'we buy cars' but they pray on those they can't afford and I will probably offer less.
If he can't do a real private deal, maybe get a dealer to broker a deal for him for 5-10k extra?
Though, 290k is really high ...
He paid 270k for a E90 335 BMW with 192k on the clocks. That was the first mistake.
Does the insurance have shortfall cover?