]I agree 100% that he should have checked post quality, but I am not aware of any basis for checking for plagiarism in 2015. If he had gotten banned for spamming in 2015 that lasted a week, I would be on the same page, but it is 2019 and his ban is ~8 weeks and has a 102 week sig ban.
It is my understanding that sig spammers were generally receiving a 3 or 7 day ban for a first offense back then, not the 60 day ban plus a 2 year sig ban he received. I am also not aware of anyone receiving a ban for insubstantial posts with a paid sig well after post quality has improved.
With regards to not knowing to check for plagiarism in 2015, I get where you are coming from, but I think thats just one of the risks of buying a used account. If a scammer sold their account before the scam accusation was made public, the new owner would get a raw deal from buying the account. I'd essentially equate it to Bill getting scammed by the account farmer, again assuming the story is true. There isn't really a way for the forum to handle it, rather than just saying, hey that sucks. I'm assuming you've read at least a handful of ban appeals where the people claim to have never done anything wrong, outraged about their false accusation, only to have someone skim through their posts, quote what got them banned, and then they go silent. Imagine what the hundreds of accounts banned for plagiarism would try if there was an inch to give regarding responsibility for actions made by an account.
My personal opinion assuming that there was a single case of plagiarism and we aren't all looking past another 15 offenses that weren't made public, is that the sig ban should stay in place and the 60 day ban should be removed. That said, with the people that are having their permabans removed, aren't they getting off with just signature bans? That leads me to believe there may be more going on than we see. Its tough to compare the punishment from 2015 to now. Sig spammers that plagiarized in 2015 just got nuked, but thats also because there weren't higher ranked members that plagiarized.