If the buyer doesn't believe what Tesla says then nothing will help. The truth is that a safety issue could conceivably, tomorrow, mean that Tesla halves the range of all its vehicles. Let's say they discover a serious safety bug in their software, perhaps under certain unusual conditions the batteries may explode. The only quick fix is to go way conservative on range, limiting the amount of charge. What do they do? What do you do?
It's easy. They put out a mandatory software update with a promise to fix the problem as quickly as they can. A few owners say how nice it is that Tesla is taking care of them. But most scream and whine and threaten to sue and so on. Tesla's reputation takes a big hit. The stock temporarily plummets. Pundits wisely intone the doom of the BEV. The non-participants buy popcorn. Eventually Tesla finds a solution and restores things to (almost) as good as they were.
It is to avoid such a situation that quality assurance on new software and hardware at Tesla is so rigorous. It takes time for extensive testing. The system is both complex and closely coupled (an engineering term meaning, more or less, that seemingly unrelated parts affect each other more than one may expect). This means that you're never really sure you've got it right, so all you can do is mitigate risk as best you can. Tesla is both blazing new trails in hardware and going further into software control than anybody else -- this is very dangerous territory.
I am very happy to let others be the early adopters on things like the D. I'm happy to wait for Tesla to say it's gotten various autopilot features right before releasing them. And I'm okay with trusting Tesla to do what it says, although I never count on its timelines. If you are unwilling to trust Tesla, you really shouldn't be owning their cars. If you want the latest and greatest and insist that it works perfectly, you are destined for unhappiness.
The only accurate information that Tesla could provide up front is "We don't know. We'll get there when we get there." The rest is speculation and noise and hope.