Not knocking or trying to be disrespectful. But what's the deal with the replica cars people are doing in the marketplace? Are they just a paintjob, some aftermarket parts and tuning them to represent a real life car? Just trying to get my head around them.
They've been tuned to look, drive, and have specs as close to a real car that is not in the game as is possible. Most of these are based on tuner cars, but others are on production variants of some of the cars that are in the game, or other configurations.
There's a whole bit in the tuning section devoted to them, and many are quite slick on the track. In any case, it's nice to have a real name for the tuned car that you're driving.
They aren't. You can recreate them yourself or with the info in the tuning forum. People selling them are just trading their work to someone who would rather be lazy and just get the benefit. Capitalism has worked like that for ages.