The highest bidders get a share of the vote , if you're the only bidder in a window you get the whole amount.
If 4 people pay the same amount they get a 4 way even split.
If some bidders pay a lot more then others, there is a chance that the lowest bidders in a round have such a small % share that it won't be worth doing - in this case you sacrifice your 0.001 SBD and no vote will be sent.

It's a risk, but a tiny one - I'd say at least 90%+ of the users end up having a positive experience from this bot.