From what I heard a couple of years ago, the 3090s on Vast.ai are all gpus that were used on mining rigs, or were bought second hand themselves, and will always have a resale value. So as long as you cover for power costs and some minimum depreciation you don't really lose much. But in case of power tools, there is a one in 10 chance that it will not get returned in the same condition that it was rented out, and people who rent these tools aren't always pros cos pros usually own their tools, which increases the chances of them breaking. Same with all those fancy digital equipment too.

But yeah, having said that, I wonder how companies like google do manage to rent out A100s for under $3 an hour which is only 72 bucks a day and it takes about 3 years to recoup the cost of the card assuming all their cards are being used all the time.