I've read the posts on here about the duping out of curiosity but have played the game straight, since I want to play the game for what it is, not take advantage of a loophole that gets me to complete the game quicker. What's the point in that? I don't want to get to 100% complete any faster than my current progress?!
Aspec25
Bspec7
60 cars P + S
Not sure about others, but i guess i'll answer anyway.
I didn't duped/bday glitched/traded even once before i've reached the point, where the game kinda ended for me. Yep, level 30, did the vettel challenge and that's it, game over. 9hr/24 hour races.. no thanks, b-spec.. same.
More than that, i actually had 12 good cars from the start (stealth + chrome ones), i didn't used any untill extreme events, and i bought a normal 787B anyway (love this car ), so doesn't matter.
So i'll say for myself only, i've duped/traded a lot of cars just to get at least 20 - 30 more hours of gameplay time. Because no way i can spend a few days on oval just to buy a car, drive it once in practice mode and never use again. So, thanks for the duping i actually tried a lot of cars without mindless oval grinding.
I don't understand people who are duping from the start, to use an X1 on sunday cup, it will make this uber short game even more short.
But i do understand people who are doing that to get cars for fun or even online. If the system is broken... people will find a way to fix it somehow and GT5 money/grinding system IS broken.