This made me wonder about business models like those of some miner-heaters that use s9 or similar. I can't say I'm familiar with mining economics or hardware to comment on this, but from the perspective of a consumer, I'd be willing to take certain calculated risks/discounts/premiums for repurposed hardware used in new products.

Like you say, the after-sales part is a factor. I'd never expect much from warranties, and I generally overlook it when buying new hardware. I feel you just have to trust in the information you are provided at time of purchase and reputation of manufacturers. But this does lead me to think that distribution of resellers is a problem. Getting things shipped from far away is a problem, repeated tax on top of shipping is probably another. If there were affiliated distribution networks for used hardware, in the same way you might have 'authorized dealers' and 'repair' for other refurbished electronic consumer goods, that would solve a lot of problems for the industry.