Dealer trustworthiness

Hello.

I was shopping used cars. I noticed most(554 out of 724 cars) of a particular dealer's cars had a dealer rating of ? uncertain. Their cars are consistently and dramatically underpriced. 7 out of 7 reviews of the dealer are positive.

I've googled/binged both the dealer and the owner for problems and haven't been able to find anything shady. I know I can use VIN#s to research cars I am interested in. This leads me to 2 questions:

1) Are these vehicle history reports reliable (I know nothing is 100% full-proof)?

2) Is there any reliable way to check on a dealer or it's owner?

Thanks.