I agree with the other reviews about researching other extensions, but found EZ Autos to live up to its name and boundless features.
A recent client needed a special feature installed beyond to make it a "set it and forget it" website using Nexteppe (www.Nexteppe.com) auto feeds, so we used EZ Autos as our base to get this done.
With some initial emails back and forth with Kathy Strickland, who was very helpful and quick to respond, we were given the green light to tweak her code if necessary. We are still adding features but our client is VERY pleased with the results so far: http://www.automarket1.com/
If your looking for a Auto Market script with excellent support and very clean code that doesn't touch the Joomla core, then look no further!
Big props to Kathy! ;-)