There's been a long running discussion about the ethics of travel writers accepting "freebies" and it's an issue most professional travel writers consider a non-issue. Most travel writers accept free or subsidized travel since the industry does not pay enough to first pay all travel expenses and then write and sell the stories. A free or partially free trip or hotel room does not necessarily mean that the travel writer will give a positive review, but in most cases only means that the service will not be mentioned. It's all covered, once again, in a recent post by a travel writer in Texas.
Subsidized travel is controversial and lots of very ethical and pious journalists look down on me as tainted and corrupt because I do it. Fuck 'em. It's a debate I don't bother getting into anymore. Suffice to say that I can't be bought. I accept only trips I think I can sell. If something isn't worth writing about, I don't write about it. I include negative impressions in larger stories when appropriate but rarely write completely negative stories not because I am beholden to anyone, but because they don't sell. Editors with limited space don't want to squander it telling readers where not to go.
I'm an ethical person doing my best in a squirrely field. A lot of newspapers pay peanuts but don't accept stories from subsidized trips. A lot of newspapers have a don't ask-don't tell policy about subsidies but if you get "caught" you're in trouble, not the editor. Many magazines are less stringent in their policies, although Conde Nast Traveler and Travel & Leisure are among those with strict no-subsidies policies. They pay for their reporters' travel. I cracked T&L once a long time ago but got tired of the effort it took to get back in and haven't tried again in many years.
By stating here that I sometimes travel on subsidies I have ensured that I will never write for The New York Times, which claims never to accept stories from writers who have ever accepted a subsidy. I have heard differently from many publicists, who claim to frequently spot stories in the Times by freelancers they have hosted. Nobody will ever go on the record with that, though, because nobody wants to piss off the Times.