I knew which car it was before clicking on the link, having just finished looking at it before coming on here.
Good spot on the paint drip on the tyre, as the wheels were supposedly refurbished a year ago?
Might be perfectly innocent, touching up a bit of a kerbing maybe, but certainly a reason to look for other signs.
That said, if all he says is true, and he can back it up with the paperwork, it sounds a cracker.
Only other obvious thing is, I saw no mention of service history, apart from what he's done himself.
Oh, and insist on the car being stone cold when you test drive, as that's when any problems with the lpg system tend to be more obvious, particularly on switch over.
Hope it's as good as it sounds, and you drive it home, best of luck.