I have just added this very feature into the Post Promoter voting bot software, however it will be up to the individual bot owners if they would like to implement it. They make more money if people overbid.
As of right now the @postpromoter bot will refund any bids that come in if the ROI is less than -10% as I think that is a good number where you still get a decent overall return from the increased visibility to your post.
If more bots adopt this feature then I will add a new indicator to the site to easily see which bots have an ROI limit and which don't.
Genial @yabapmatt, me parece bien que estes trabajando en esto, se te agradece al menos de mi parte por tu trabajo, te apoyare en futuras ideas. ademas ya estoy siguente como testigo. saludos :)