I think a more gradual solution could be achieved by requiring the bid botters to decline rewatds so the bots function is more promotional in nature.

The problem is that you can't actually reliably detect bots. So you cannot reliably detect bid bot users. Anything attempted to do to detect them is looking for a pattern. All they have to do is change that pattern. Also doing this it becomes increasingly likely people that are not bots or accounts that are not bots will be false identified as bots.

This is NOT something anyone out there has reliably solved. If they did they'd have a high million or even billion dollar product.

This is why captchas exist. They do not detect bots, but they make a barrier it is difficult for bots to solve, but easy for humans.