Multiple journalists over the past several months have publicly denied shilling for Hillary Clinton. And they aren't lying: one of the main design principles of a good sell-out is to arrange it in such a way that no one thinks they're doing anything wrong.
Unfortunately, it's pretty easy to put together the sort of "ethical" shilling operation that people are able to rationalize to themselves (and to their bosses and attorneys, as necessary). This is particularly true since even educated people often have fairly cartoonish and conspiratorial ideas about how media corruption works - which means that they're often extremely inept critics. When a random skeptic accuses Peter Daou of taking money under the table for giving sympathetic coverage to Hillary Clinton, he has no problem with denying it (since that specific transaction didn't actually happen).
But none of this is to say that anyone's hands are clean. Of course journalists are shilling for Clinton - and of course they're doing it in a way that gives them plausible denial. I know this is true of particular journalists, but I also know this because I've built political messaging operations myself. A few basic points:
1. There is almost never a formal quid-pro-quo. That is the sort of thing that gets journalists fired and campaigns fined. Messaging campaigns are less concerned about this than they used to be - the FEC can't enforce anything, and the public is so numb to corruption that it simply isn't as scandalous as it once was - but most are still built around the imperative of avoiding formal agreements. Instead, the transaction is generally implied, taught, or simply understood.
2. There is almost never an actual monetary bribe, for all the same reasons given above. Instead, journalists are usually given perks, access, and potential opportunities. Perks range from the relatively trivial (free drinks) to the extravagant (free travel and accomodations). Access includes dedicated and responsive points-of-contact, exclusive interviews and scoops, event invitations, and so on. Opportunities usually involve future job openings or unspecified favors that may or may not actually materialize.
3. Individual journalists are usually in the dark about most of the messaging operation. Strategic objectives are usually determined by campaign officials at a fairly high level; those are almost always kept internal. Media liasons usually only convey particular messages, but they don't brief journalists on the goals those messages are meant to accomplish - and journalists, who prefer to maintain a pretense of blissful ignorance, usually don't ask.
4. Messaging is rarely dictated. Often, campaigns will present their angles or talking points as "scoops", "tips" or "interesting topics" that journalists can voluntarily report on in their own way. When tighter control is needed, they'll often provide carefully phrased statements or quotes. Message discipline is cultivated by selecting sympathetic journalists and enforced, as needed, through flak - a notorious Clinton tactic.
5. Often, instead of disseminating their messaging directly, campaigns will launder their efforts through some nominally unaffiliated third-party - which allows both the media and the campaign to deny any coordination with each other. The Clinton campaign and Correct the Record, for example, have openly defended their right to coordinate messaging, and it's not difficult to imagine how those efforts might be reflected in, say, coverage in David Brock's Blue Nation Review.
This is just a sample of the approaches that modern political messaging operations use to get around public scrutiny, campaign finance laws, and guilty consciences - but the M.O. should be clear. By keeping transactions informal or implicit and communications indirect, campaigns can exercise an extraordinary amount of control over the press. Journalists, meanwhile, are constantly presented with new, innovative and pathetically unethical ways to sell out. And they do.