Just read this post...ok here is your starter for ten for pricing differences
Mileage (obvious)
Condition (obvious, but not always evident looking at pictures online)
GT vs non GT
Import vs UK Car
Pre vs Post facelift
Colour, black and blue generally sell for more (can be up to £1k more) than equivalent Silver or mostly Orange
Rays vs non Rays wheels (I agree actually about Rays, they look rubbish but are much lighter, hence why I got one without Rays and bought Volks Racing instead)
Zed prices are highly seasonal, like most rear wheel drive sports cars, definitely moreso than 4WD, 4 door saloon cars I am guessing
When I was looking I saw lots of different prices, but stuck all 120 odd cars details on AT into a spreadsheet and trends became clear. Its not randomly priced or people being all over the place, most are generally on the button, you just need to do a bit more reading up and understand more what you are looking at.