This is where places like Crutchfield and eTrailer are a great treasure, and why I try to buy from them when their pricing and shipping is anywhere near what I can get elsewhere. There are so many useful tech reviews, videos, and guides from guys who spend all day everyday dealing with this equipment, they really create a great value for anyone who only has to shop this stuff occasionally.
Of course, when their price turns out to be 50% more than an Amazon marketplace seller, it's a no go. But I'm usually happy to spend 10%, or even occasionally 20% more on cheaper items, for the guidance they offer.