I have left quite a few neutral trusts for shitposting, excessive trolling and other abuses as well but I didn't receive any PMs recently to remove that neutral trust. Maybe it's just because I've explained each neutral feedback in detail or the members are well aware that if they continue their abuse (also via "unsolicited PMs"), it won't get better. If some members are admitting their mistakes, I'm always open to remove a neutral trust but I like to keep it public, for public record. The best feedbacks are, where everyone can review the evidence via reference link.


Best approach for negative Trust in my opinion as well.
If there's any legitimacy for removing a particular negative trust, it's required that the community needs to come out in strong support of removing it.
If the community doesn't come out in strong support of removing it, there's just no legitimacy in removing that particular negative trust.

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@OP
Regarding your PMs: I would review a particular neutral trust if the request via PM is really honest, constructive and the member is willing to admit his mistake. But that's also including that the abuse which has led to that trust, is lenient enough to be removed from the account's trust page.
If the PM is not constructive at all or the abuse has been simply too harsh, I would keep the neutral trust even longer.
Probably, if someone is sending you repeatedly PMs requesting to remove a neutral trust, it could be considered as "unsolicited PM spam" and could be reported.

And for your particular case, it really looks like that these people only care to get rid of your neutral trust due to paid signature campaigns.
So, your neutral trust is most likely very accurate to "warn" campaign managers about signature spammers.