That's not how morality should work.
Why do you need to "trust" someone else's morals? You judge for yourself.
It's just a dumbed down way of thinking, isn't it? So if someone rapes someone, but they say something universally moral, that moral saying is suddenly immoral because a rapist is uttering it?
Surely the morality or immorality of a particular quote needs to be construed from the message behind that particular moral itself. If you judge it based on whos uttering it or some "trust" rating then you will get erroneous/illogical results.
So let's say, for example, mo says "don't kill innocent people", by your logic this becomes an immoral saying simply because the person saying it is a rapist. Even though not killing people is something moral. Morals are NOT gauged by some "trust" rating of the person uttering them.
I've psychiatrically evaluated convicted murderers lol, even they have uttered some surprisingly positive morals. The meaning behind a moral remains the same, just because it was a convicted criminal who believed in this moral doesn't suddenly make it immoral nor does it mean any other of his behaviour is immoral. Behaviour needs to be judged independently.
I can't remember the exact psychological term for this fallacious logic, but it is fallacious logic.