Let's take the whole spammyness of the affiliate links out of the equation, and what this boils down to is just vandalism. Vandalism on any of our sites will quickly get you suspended or shown the proverbial door, so we highly recommend not doing that, or anything else, that intentionally lowers the perceived quality of our combined work.
Don't trigger on just seeing an affiliate link of some kind - some sites give you sharing buttons automatically encoded with affiliate information even if you're not part of the program, and folks don't even realize what they're pasting - they just think it's a link.
Trigger on the perceived intent when it comes to vandalism. If the person is doing it serially, and it's hard to argue that they aren't aware of how inappropriate such a thing is, then we will take very swift and decisive action. But, that's up to the moderators and us, the community team.
Remember that the whole point of suspension is to get problematic behavior to stop, and suspensions should last precisely the amount of time needed to make that happen. I don't want to get into territory where we set up mandatory 'sentencing' for different kinds of infractions.
However, I will say this, if you deliberately and repeatedly vandalize one of our sites, you're going to have a pretty hard time convincing us that you should be able to access them at all beyond reading, and we've got pretty comprehensive facilities in place to make that happen.