[evilduck]

Two and three are really the same problem and are solved by periodically running the same workload in duplicate on other systems and comparing results to detect unreliable sellers. Same as all the captcha systems. It's an overhead required to have trust built into a system. In the event of a faulty GPU, the owner would likely want to know anyways.

The first issue could be addressed by just never giving a seller enough data from a buyer to abuse, but that does require a critical mass of both buyers and sellers before you could distribute and dilute a single customer's workload enough. The company could bootstrap this with renting their own GPUs and subsidizing sellers at first though.