No large company cares even a tiny bit about the money they're spending on bug bounties. They would literally lose money trying to cheat, because it would cost them more in labor to argue with people than to pay out. In reality, the bounty teams at Google and Apple are incentivized to maximize payouts, not minimize them.

If you don't trust the company running a bounty, don't participate. There are more lucrative ways to put vulnerability research skill to use.