You absolutely can't offer someone money to steal documents. That's clear. Even providing advice on acquiring documents is probably going to be unlawful. And if possession of the document itself is otherwise illegal (i.e., CSAM) there's no protection there.
It isn't necessarily illegal to offer money for a document, particularly if you don't have knowledge of how the document was acquired. I'm not familiar enough with this case to have a strong opinion other than knowing the DoJ elected not to bring charges.
And, yes, it was Trump's DoJ. In this case I'm unaware of any evidence that the decision was politically motived and I still have some confidence that whistleblowers would speak out, particularly given the recent wave of resignations due to directives in Minneapolis. I think people of good will could disagree with me there for sure.
Most courts would assume someone who purchased a private diary of a living person would know that it was stolen.
Prosecutors don't need to prove the buyer actually dispositively knew the document was stolen, only that reasonable person would have known it to be such.
Which would be obvious in this case.
But I appreciate you iterating on this -- I understand your position and while I disagree with you on the question of what "reasonable" would be in this case, I absolutely think that if I could read minds I would find that Project Veritas staffers at the very least knew the diary was stolen.