Jon Blaze, welcome to GTPlanet. I'm John, from Houston, TX, USA.
As reported in the GTP thread "Gran Turismo Resorts," secondhand car dealers will more likely be accessible in allowing used cars. And this is a blessing since you had to buy a new car from a dealer. And since 10,000 Cr isn't enough, you had to start with 18K Cr. And if you're a loyal and respectful and honest person, you won't rely on GameSharking to complete GT4 at 100%. This has been mentioned long before, so in the future, try to search more often to avoid being flamed on with "use a search" talk. Having said that, nice to have you on GTPlanet. Farewell to you.