When it comes to glitches, you should tread carefully. Not only do the devs usually patch out these little bugs from letting you gain an advantage, but sometimes, players will be penalized for performing them.
Nevertheless, YouTube user ProKrieK has uploaded a glitch that allows him to resell his car constantly to Los Santos Customs, making a ton of money in the process in a relatively short time. This glitch only works on the Xbox 360 version.
According to ProKrieK, your car should be valued around $15k-$20k, and shouldn't be valued over $50k since LSC won't buy it from you. Navigate to the Sell option and sell your car. Immediately afterwards, press the Start button and navigate to the Xbox Games Store tab and press A. Once it loads, press B to back out into your game again and your car should still be there, allowing you to keep reselling it.
Again, tread carefully when it comes to Glitches, and remember that sooner or later, this glitch will probably become useless as Rockstar will inevitably patch something like this out.
