wow. sorry to hear.
as the other members already noted:
05 GS vs 05 Coupe off the top of my head:
exterior: more aggressive front end, added orbital shape side skirt, (red Maserati sport emblem), trofeo wheels
interior: GS sport seats, different dash, different headunit, carbon center console, carbon/leather steering wheel, "Gransport" emblem on dash, blue dials with Maserati Gransport, footwell entry plate says "Maserati Gransport"...
characteristic brightex fabric on early GS.
mechanical: revised shifting program (35% quicker), 10mm lower suspension, active sport exhaust (via sport button) made by tubi, extra 10hp (freer flow exhaust), (rumored to have even higher hp)....
may be you havent ever seen a Gransport... you can perhaps see how it looks different:
http://motors.search.ebay.com/maser...mZR40QQfsooZ1QQfsopZ1QQsacatZ6001QQsamcmZ6001
may be your sport seats were part of the 'sport interior'?
vin and chassis number, they should be sequential for the cars, and not particular to coupe/gs. they would probably be all mixed in. only the dealer should be able to tell on their computer.
please add to the nasty letter that you suffered from the humiliation on a message board because of their lies.