No. The entire advertising industry would collapse if that would happen.
Sure, but I think the answer isn't as absolute as it might sound. If I advertise a service, aren't I considered an employee of that service? Or aren't I an employee at all? Am I considered working for somebody else? Am I subjected to the integrity of that else?
Purely hypothetical, but let's say either Betnomi or ChipMixer does money laundering (without the acknowledgement of their campaign participants). Are participants considered guilty, from a legislation point of view, for accepting laundered funds? We don't sign any legal documents when submitting the registration form, and I'm curious how far can the authorities reach this.
You could be considered "affiliated" by accepting payment for advertising the service. I think that it is highly unlikely that an authority would reach their arm all the way from the founder of the service, to those who work on it technically/directly in some way, to those who manage campaigns, then to you, just for being paid a few dollars per post to have some flashy text in your signature. I doubt the arm would even reach as far as the campaign manager. As LoyceV said, the entire advertising industry would collapse if things worked that way and if it worked like this at maximum efficiency, the population of incarcerated versus not would probably be way out of balance.
If you are worried about being prosecuted for being very slightly and temporarily affiliated with a service that is very likely to have some users that are using it for illicit purposes (which is almost certain with mixing services if I'm not wrong), then don't. If you were ever prosecuted, it's probably likely that it's not the primary reason that whatever authority responsible was coming to you. I would assume (take with a grain of salt) that you'd have nothing to worry about if you aren't already under watch for a much more serious reason and/or you are doing basic things to sufficiently upkeep your privacy.
