Why some used cars adverts are very cheap in NY Times auto? Wondering any trick behind those private sales?

I’m looking for a used car at reasonable price and I found some of the private sales on NY time are a lot cheaper than dealership sales. What should I be careful about buying those cars? Is Carfax report enough?

What are those little things on the hood of custom cars?

Well I was watching this show on tv where they make junk cars into custom show cars and on the hood are these little circles with strings or wires going into the engine. I was just curious to find out what these are? Can anyone help?

If auto makers are having so much trouble, how do they afford all those TV commercials?

The auto makers say they are having financial problems yet there is no shortage of TV commercials! How do they afford to put out all those commercials on TV?