I don't think that shutting down the whole campaign makes sense since that would in effect be equal to cancelling signatures altogether in the most indiscriminate way. It is obvious as well that
not all users enrolled in this campaign are evil spammers, but this doesn't in the least mean that there are no spammers without any signature, either.
Ever hear of the saying "A few bad apples ruin the bunch"? That is exactly what is happening here. If those users who are not shit posters actually post with decent quality, they should have absolutely no problem finding another signature campaign willing to both pay them more and accept them into the campaign.
It might well be the case that this service attracts the greatest number of shit posters across the forum, but this alone doesn't make it anywhere near guilty for them posting outright spam. Since you can always find a number of die-hard spammers who wear no signature at all. On the other hand, nothing prevents all these Bitmixer.io spammers from starting posting sense (or at least refrain from posting garbage) if they really wanted to. As you can see, their failure to comply with the quality standards of the forum is not Bitmixer.io's fault...
It is entirely bitmixer.io's fault for paying the shit posters and not enforcing their own anti-spam rule. It is entirely their fault for enabling those shit posters/account farmers to continue to post and be paid for it. They are encouraging shit posting by continuing to pay for it; and that is entirely their fault.
While yes there are still spammers without sigs, most spammers that I have seen do wear sigs and they shit post because they have an incentive to shit post; they are still paid for those posts. Furthermore, it is known that many campaigns are lax about who they accept, so newer members without sigs still shit post so that they can get to the right activity requirement to join one of those campaigns. Again, they are all motivated by being paid for their shit posts.
If it is known that the forum staff will harshly crack down on signature campaigns who allow their participants to shit post and do not properly check new members, then a lot of spam will be cleaned. Campaigns that enabled shit posters will be shut down, thus the shit posters will either have no incentive to post anymore or they will have an incentive to post constructively in order to join a campaign with higher standards. Furthermore, newer members will then have an incentive to post constructively in order to join the sig campaigns. The bar will be set higher, and thus post quality will increase.
Given that, these spammers should get banned just like any other spammers here
Many are, but many still continue to shit post after their bans or they come back with alts to complain about their bans. However there is enough evidence to suggest that many of those spammers spam because they are being paid by poorly managed campaigns. Thus instead of treating the symptoms of the problem (i.e. the spammers), we need to treat the source (i.e. the campaigns themselves and the people who run them).
About punishing the services as well as the campaign managers: this is because the campaign managers are hired by the service. Most services advertising here have a forum account. They hired a campaign manager to handle their sig campaign. If a campaign for a service is to be found to be spamming, both the service and the campaign manager should be notified. It is up to the service to fire their manager and hire someone else who can do the job better. If they do not, then they are not doing anything to help even when warned. Thus, the service should also be banned from using sig campaigns for advertising.