This shouldn't be much of a problem to do but it might be helpful to those who wish to trade their cars for items instead of cash.. There should be Car keys that you can trade in the trade window, it'd make things easier and staff less likely to be bothered, even though they're probably just screwing around anyways.
Oh and that car engine you guys added in... Really SUCKS. Its to repetetive and it gets annoying listening to it keep reving when you're already at max speed.