I once made my own bot tracker program, which was quite accurate but suffered from one problem. The problem was that for a round, my bot tracking program saw the bids until the point where the bot started voting. Now, if someone bid while the bot was upvoting, that bid was ignored. This is also the reason why 
So, my question was, which bots should you prefer when asking for votes. I would say the ideal bots should have the following characteristics.
They should provide an API that guarantees 100% accuracy, like I discussed above.
They should automatically refund invalid bids. This is because human error is possible when asking for a vote, and if a bot doesn't refund invalid bids, you can lose significant amount of money.
I have seen some bots, who hang up at 100% if they don't have enough bids. In my opinion, this is cheating. I note down the names of such bots and never ask vote from them again.
What is your opinion on bid-based bots. What do you think are characteristics of an ideal bid-based bot?