How do you handle the risk of not being able to resell instances that you've bought back? What if I buy 10,000 instances and sell them back to you after 30 days? Seems like a competitor could do something like that to intentionally sabotage your business. Though maybe there's so much liquidity in the market that this isn't much of a risk, and in the worst case you could probably find someone you could sell to at a loss.