Steve,
PPC has 2 prongs of attack.
#1). Ads that appear for Broad terms like 'Used Cars for sale', or, 'best price on a nissan', etc.. (aka "Short tail")
#2). Ads that appear for what ever you have in stock only like your
2008 Chevrolet Avalanche 1500 (aka "Long Tail")
Your lowest cost and highest ROI will come from the #2 ads. HayStack and TDC will do this for you. These "Long Tail" ads will perform well, but, will have a low volume of traffic (relative to "short Tail" ads).
WARNING: There is great danger of burning thru cash if you set the '
Broad/Phrase/Exact' controls incorrectly. I know where you're coming from, your goal is to improve the results and understand how it works but "tweaking the knobs" can bring a jump in traffic, but, do you really know what traffic you've created?
Example:Chevrolet Avalanche.
Set it wrong and you'll be bringing in traffic related to Avalanche (as in snow and the touring band)
Example:Chevrolet Avalanche.
Set it wrong and you'll be bringing in traffic related to Chevy Avalanche floor mats and wipers and recalls and air bags and replacement body cladding for a 1999, etc...
If you really want control, there are thousands of variables that you must understand and conquer. For example, it took me WEEKS to build a 'negative key word' list. If you want to persue this, I HIGHLY suggest that you run 2 campaigns.
Campaign #1 is let TDC or HayStack run with the ball on both the long and short tail campaigns.
Campaign #2 will be DIY, but make it a small and focused campaign with the intent to grow and learn. Re: DIY. If your negative keyword list isn't at least several hundred keywords, then beware broad matching anything. Also if you don't know what a Broad Match Modifier is, then acknowledge this and keep your DIY budget tight tight tight and use it as a learning tool.
HTH