How did customer get a list of all the equipment he would need and realize it would be cheaper online? Did you give him a detailed shopping list with a break down on prices? Did you at least charge him a design fee? This doesn't help now, but maybe it will in the future. This has been gone over here many times.

As far as warranty, I doubt Crestron has any authorized e-tailors, much less any on e-bay, so there would be absolutely no warranty. I'm sure their policy goes something like, "sold and installed by authorized dealer" to be under warranty.