The reason you don't see much talk about it is because how detail oriented it is. I consult on a few different specialty part websites, mostly racing stuff, that has more forgiving margins. We can play the game because of less competition, and good margins.
When you are talking about specific parts you need to have a solid understanding of your profit margins, conversion rates and cost per acquisition. Your website needs to be optimized for ecommerce.
Point being, it's very hard. You would need a website dedicated to parts, and someone managing it that is willing to spend hours every day optimizing it for seo, sem and conversions. That is not what you will find from an OEM campaign manager. Those companies are probably capable of doing the ppc portion, but you would be far better off with an outside company specializing in ecommerce.
If you want to bid on your generic local searches, such as "auto repair Boston, " you can get that anywhere. Your cost per click will be pretty low, and you could use your current site with a few tweaks.
if you want to play parts with Auto Zone you will need an expert. Not a $350/month bid manager.
