Perhaps we are looking at it the wrong way. Ban the campaign managers and the projects that hire them if they use people who are using spam bots and give everyone in the campaign a warning that they were working with spammers. After a certain number of warnings you would get a ban. Would that be too harsh?
Nope, not too harsh at all. In fact, doing exactly this is already in the rules stickied to the top of the Services board:
If you are running a campaign and it becomes blatantly obvious to Staff that you are doing little to nothing to stop spam on your campaign you will be issued a PM warning by a Global Moderator that you need to make immediate improvements to curb low-quality posts. You will have 7 days to remove low-quality posters and respond to the message detailing what you are going to do to make changes to your campaign to reduce the amount of spam. If improvements are not noticeable within 21 days of that and Staff do not believe you are doing enough to prevent low quality posts your signatures will be blacklisted from the forum by an Admin and you will no longer be permitted to advertise here in such a way.
As far as I am aware, this has literally never happened. Even when we had the absolute flood of YoBit spammers, it took months of the forum being an absolute shitshow and multiple threads in Meta and Reputation complaining about it before we finally got some intervention.
Just enforce the rules. 7/14/30 day escalating bans for 1st/2nd/3rd offenses for spammers, followed by a permaban. Same for campaign managers and campaigns themselves. Actually do this and the problem is solved. Spammers are banned, and new spammers joining are massively reduced because there is no incentive for them to do so, since any campaign manager which accepts them will also be banned. Campaigns are incentivized to use good campaign managers, because if they choose a bad one they will also be banned from advertising here.
The solution already exists. It's just the mods and admins ignore it. I don't know why.