There could be clear cut guidelines in place that if you use @buildawhale for something like this, the vote will be pulled and the person doesn't get a refund. If you've already taken money from people that are blacklisted in the past and not returned it, I don't see where expecting you to pull a vote from garbage like this is a stretch. Do you want repeat business that hurts the platform?
edit
For clarification, I'm not trying to single you out here, but most of the other bidbot operators don't really seem to give much of a shit about stuff like this. In the grand scheme of things, I understand the logic that stake weight is essentially being rented and whatever they do with it is going to happen, but I don't think anyone is going to be upset with you if you pull the vote and tell this guy that you don't want his business anymore. If you do want his business and don't give a shit, then don't bother defending yourself on the "It's not my fault he misused a service I offer" comment above. Just my two cents.
Shit posting is good for bid bots and upvote selling businesses . As long as there are shit posters that cant get exposure in any way on their own, you will always have someone buying votes.
The worse the content gets, the better off bot owners are due to a bigger pool of potential users.
There is nothing more Anti-Steem then bot and upvote services.
@themarkymark can make all the blacklists he wants but you simply cannot escape that.
Bots live from shit posting. You can have an occasional, "sure, maybe this deserves a 1000USD if it was voted for ORGANICALLY"... But it still remains that it was self upvoted. Its not really trending, it wasnt picked by the community.
There just isnt a way for bots to be used "properly" and not fail.