i just bought a 2003 ford mustang gt convertible,the car lot had it posted as a Mach 1 it doesn't have the hood scoop but does have the mach 1000 stereo system in the trunk. Is there a way to tell?

Style wise, the Mach 1 was very distinct from other Mustangs as it drew heavily from the 1970 Mach 1. In addition to the matte black spoiler and hood stripe, flat black chin spoiler, Mach 1 rocker panel stripes and Mach 1 badging on the rear, there were also faux Magnum 500 polished 17x8 alloy wheels. A retro themed interior was included with well bolstered dark grey leather seats featuring 70's style "Comfort Weave" textures, a 1970s style gauge cluster and a machined aluminium shift ball. An optional 18G interior upgrade package included stainless steel pedals, a 4-Way head restraint, aluminum finished shift boot trim ring and door lock posts, and aluminium look bezels on the dash. The most noticeable difference visually from other Mustangs was the bulging hood with cut-out and the return of a semi-legitimate "Shaker Hood". While physically identical in placement and function (the scoop is said to be built on the same tooling as the 1970 Mach 1) it only provides a portion of air to the motor routing to the air box ahead of the MAF. It does function well as a cold air "snorkel" and a partial Ram Air at speed. -- http://en.wikipedia.org/wiki/Ford_Mustang_Mach_1

There were NO convertible mach 1s Source: I own a mach 1

If its a convertible it's not a Mach 1

There are websites out there where you can enter the vin an it will tell you the car specs.