The black car listed by Naples Motorsports is legit as far as I know. Naples Motorsports is a very reputable dealer and has sold many used NSXs.
The silver car listed by a private seller with a zero feedback rating, however, has been listed on eBay previously under the VIN number of JH4NA1155MT002607. The story about the salvage title changed from water damge (from leaving the window open - HAH!) to theft recovery. I see the current ad still says theft recovery, but there are obvious signs of poor repair of considerable damage in the pictures.
The photos in previous ads for the silver car showed a serial number plate of 002229 so there was a VIN issue even in those previous listings (listed as #002607, shown as serial #002229 in photo). Now it is listed as #001777, so it appears the seller took the VIN number from ad for the legitimate car listed by Naples Motorports and used it for the latest listing on the silver car. I'm quite certain the seller would not be able to produce any photo of the silver car with that VIN or serial number plate!
It's really funny that the seller gives you a link to the carfax for #001777 because the history on that VIN does not match the sellers description of this car at all (there is no salvage title for #001777).
www.carfax.com/cfm/FSBO.cfm?report=CFX000004535869
A carfax report on JH4NA1155MT002607 does not show salvage title either and, like #001777, that VIN was probably just taken from another ad.
The VIN for 1991 serial number #002229 is easily determined - JH4NA115XMT002229. The carfax for that VIN does show salvage and odomoter rollback and thus at least matches the sellers description of the car. See
http://www.nsxprime.com/forums/showthread.php?s=&threadid=20825
While #002229 may be the true VIN, I'd still like to see the other VIN plates and the engine number from the car before I would be comfortable with that. I'm not sure why the seller would mention in the ad that the car has a salvage title and then provide VIN numbers from different cars that do not. Maybe someone should call him at the listed number of (415) 859-0872 and ask.
For previous discussion about this car, see these threads:
http://www.nsxprime.com/forums/showthread.php?s=&threadid=19499
http://www.nsxprime.com/forums/showthread.php?s=&threadid=18719