I have bought several things from etrailer.com (2 towing hitches, a roof rack, snowboard rack, bike rack, rooftop cargo box, wiring for hitch mount, etc.). The products are great (brand names like thule, yakima, and others) and are priced very well. The site has all sorts of info for figuring out which items will fit your vehicle and then provides guides for installation. The guides are not factory ones, but ones written by real people who have installed the very same thing. The site also tells you which other items you might need in tandem for proper installation.
The shipping was very quick, I even got upgraded to faster shipping for no extra cost this last order (bonus since I would have been just fine to have gotten it in 2 weeks rather than 1 at Christmas time). I got emails every step of the way: confirmation of order, shipped with tracking info, and a final email from an actual person telling me that UPS informed them that the item was delivered to my door and that they wanted to verify.
They'll e-mail you to ask you to fill out surveys, but it's not much to ask when compared to the horrendous experiences I've had with other retail sites that have asked me for comments. I'll take a minute or two to help out a company that has enabled me to haul, pull, and play by outfitting my cars for years.