I just lost a customer who purchased through Amazon because of their free shipping. The product was priced the same except, Amazon essentially undercut my price by utilizing their massive shipping network. Unfortunately, Amazon knows nothing about my products and will provide no customer service. Bottom line price does not matter if you now have to find someone who will assemble, install, and service the product.
Amazon = low price + free shipping + elimination of customer service.
You cannot return a complete solar charging system installed on your RV. It would cost you too much to have it disassembled, packaged, and returned for a refund. You could go after the installer to fix the system, however, the installer may claim they do not warranty other manufacturers products.
Again, using Amazon will save you in shipping cost except now you have no "middle man" to take care of the problems ie: By using Amazon you effectively eliminate customer service.
This is all good if you can afford disposable, single use products.