Speaking from experience, turning down trips/gifts and holding companies accountable (which they'll inevitably view as unfair) leads to being shunned. Which has been fine for me as I much prefer being outside of that circle. It's pretty evident though when they won't even respond to emails regardless of the topic even if it's something as simple as requesting comment on an issue (which typically they would like to interject in a story).
It's as though they expect someone to beg if they're not included in getting invited to events, early copies, interviews, or the like. Almost as though they believe - and some outlets probably prove it to be true - that if you go it without them you're going to be doomed so you have no choice but to stay in their good graces in whatever way is necessary. They don't know how to deal with an individual our outlet who doesn't feel as though they need them to provide valuable content to readers. If anything being able to stay independent from their reach while building other sources and providing relevant news and analysis with proper evaluation (and an avoidance of influence) has proven to be a level of differentiation that has helped sustain and grow a following. It's ironic in a sense.
It's important to never compromise those values and know that the readers are who you're servicing and avoid becoming an arm of PR. Unfortunately it seems there aren't enough of those people/outlets out there who have proper self control or respect for the field they're covering. The relationship between writers and PR is something that should always be closely scrutinized.