Exactly so. The rule of thumb for a writer ought to be: if you wouldn't want your readers to know you're doing something, don't do it.

A travel writer is more or less a journalist. He or she is supposed to be dispensing information and opinion without the influence of outsiders. IMHO a travel writer accepting comps or insider's freebies from certain travel providers is not much different from a New York Times political-campaign reporter accepting money or perks from a certain political candidate. You wouldn't take him -- or the Times -- seriously anymore. It's not ethical.