For some, the kit will be good enough. It will produce enough to cover their needs and they will neither know or care that it could be built better and produce more. They get a great deal.
Others will buy it, find it less than they need and will replace everything but the panels to get what they need. They spend a lot of time and extra money that a little knowledge would have saved.
There is a lot of knowledge here, you just have to provide the numbers and believe me, these guys like to spend your money. You may be back to the drawing board, but at least this time you have chalk and an idea of what to start writing.