Zero used to offer very good customer service, at least through 2012. During that year they picked up my bike twice from my home and repaired it at the factory and then later in the year sent me a large Zero-brand backpack out-of-the-blue, which I still have in my backpack storage closet.
I guess vehicle sales have outrun customer service now, especially when you are some distance from the factory.
Having had 25 years and a number of warranty claims regarding 8 BMW motorcycles that I have owned over that period, I can say that I have never had to argue with BMWNA about a warranty claim. My dealer always did that and always managed to get approval for the warranty work, even when it wasn't covered by the warranty contract - such as when my steering bearings (a "wear" item in the warranty language) failed on two different motorcycles and another time with my original battery died after two years and was replaced for free with a new battery.
But (having said that) it takes even BMW time to find the parts in their inventory, especially in North America. If my computer-controlled "semi-active"
$2,900
rear suspension unit failed it would likely not be found in their parts inventory and would have to be special ordered directly from the factory and that would likely take about 30 days to arrive. (BMWNA tends to stockpile small, relatively inexpensive parts, but the big expensive stuff they won't import unless needed on a case-by-case basis.) Also, while my BMW dealer will give you a service loaner bike to ride for a day, they won't let you keep it overnight, much less until your bike is finally repaired.
My suspicion is that Zero orders just enough parts from their off-shore suppliers to manufacture the number of motorcycles that they plan for the year and just doesn't order much in the way of extra parts that may be needed for warranty claims. When something like a failed shock (I had two new Ohlins shocks completely fail over the past years, both of which needed to be rebuilt by the distributor), occurs, Zero likely doesn't have any extra shocks just laying around and then comes the stonewalling. If they don't have any extra shocks, then the smart thing to do would be to authorize a local motorcycle suspension shop to repair the shock. Since they are using Showa components now, instead of goofy Fast Ace stuff, it should be no problem to have the shock repaired locally. It could be repaired quickly, paid for by the shop and let them fight with Zero to get reimbursed. I imagine that their franchise agreement would provide for situations like this.
Alternately, the customer could go the same route and if Zero didn't reimburse them for the cost, they could sue them in small claims court and that would be an easy win, I would think.