The optional extras on the car are:
1. Cruise control
2. Parking sensors
3. Leather seats (but not heated and headrests are not embossed with GTi logo)
All 3 of those could've been added by the previous owner. There's a sticker in the handbook with a bunch of codes on it that tells you the spec when it left the factory. My car had leather when I bought it, but had cloth seats originally and therefore has no seat heating...
http://vag-codes.info/files/options/vag-option-codes.pdf
I've checked the codes from the sticker in the boot.  The full list is below.  Note it does NOT have cruise control or parking sensors and it says Fabric seats!!!!    
So the big question, if these were all after market fitted then what impact does that have on the car value.... is it worth even less??
Code   Description
0AE   Front stabilizer
0BF   Rear stabilizer
0GG   Emissions concept EU 4
0Y1   Standard climatic zones
0YC   Weight category rear axle weight range 3
1AT   Electronic stabilization program (ESP)
1G8   Breakdown set
1KY   "Disc brakes, rear"
1LL   "Disc brakes, front"
1NL   Covers for alloy wheels
1XU   Mass damper
2G7   Filler neck module 1 with insert
2JG   Body-colored bumpers
2UC   Sports version
3S0   Without roof rails/roof load rack
3U3   Luggage compartment cover with luggage net
3YR   Door pockets with insert mats
4K3   Radio remote controlled central locking operated from inside and safe securing
4R4   Power windows with comfort operation andcircuit breaker
4UF   Drivers and front passenger air bag with front passenger air bag deactivation
4X3   Side airbag front with curtain airbag
5MD   Decorative aluminum inserts
5RV   Outer right rear view mirror: non-spherical
5SJ   Outer left rear view mirror: convex
8AG   US RADIO STEREO CR.
8GU   Alternator 140A
8ZN   Antenna
B0N   "Component parts set, complying with vehicle type for Great Britain, various parts"
CG6   "Alloy wheels 7 1/2J x 17 3B7 601 025 A, offset 45"
D2L   "4-cyl. gasoline engine 2.0 L/147 kW 16V turbo FSI, homogeneous base engine is T59/T61"
E0A   No special edition
G08   Front shock absorption
G0K   6-speed manual transmission
H6L   Tires 225/45 R 17 91W/Y tire width restricted to 219mm
J0L   Battery 340 A (70 Ah)
L98   "Suspension range 98 installation control only, no requirement forecast"
N2T   Fabric seat covering
QG1   Service interval prolongation
T59   "Components for base engine, unit 06F.C"