They are trusted because that is all they do, review products. Generally the well established, well known names are the way to go when it comes to reading any type of review.
Trusting information about something as pricey as a vehicle requires good sourcing, sound facts, and unbiased advice.
Under the new category they provide:Their top picks for the year A road test guide Previews of newest cars they can get their hands on to review
Conversely, under the used category they provide:Best and worst lists A review list of cars A to Z An owner satisfaction section noting cars people they surveyed would purchase again
Handy unbiased advice
Consumer reports prides themselves on the fact that they accept no advertising, or free samples and that they purchase each car, which they test above and beyond to provide a real in-depth review.