How damaging are potentially negative items when trying to buy a car?

It depends upon how damaging they are. Before applying for a loan, you should know what your credit history is and how you are viewed by potential lenders (FICO score). Some lenders will give anyone credit regardless of how bad it is, but you will pay for it in the finance rate. It's not impossible to get a car loan with bad credit, but it is unlikely that you will get favorable terms on your loan.