I have no idea how often it happens, but I have read anecdotal comments on HN about people having it done to them. Not too long ago there was a person. I can't for the life of me find it now, but some time ago on HN there was a person whose account got banned for upvote gaming, but it wasn't actually him. Fortunately dang let him make his case.
It happened to me. Was permanently banned and I never made use of a service like what the OP mentioned.
Now I am still using adsense but through a 3rd party that takes a large cut.
Unfortunately, this does actually happen
It should happen way more often, so it becomes ineffective.