Interesting post from Lewis Silkin about the UK's ASA versus the EU Court of Justice: the former allowed an advertiser to rely on a third party's representations (I think that's a bit of a simplification--the third party was the complainant who objected to a characterization taken from its own website! I don't know that the ASA would allow reliance on a totally unconnected third party) while the latter didn't allow an advertiser to rely on claims that it was the exclusive provider of certain booking services despite having contracts that purported to make it the exclusive provider, when it turned out that some of its partners had ignored the exclusivity provision. Due diligence, Lewis Silkin concludes, is likely to be insufficient if you're wrong.
This is the US result under the Lanham Act and most consumer protection statutes, too, though I would expect that concepts of standing would also play a big role here; it is extremely unlikely that a hotel would be able to challenge a hotel information site under the Lanham Act, though trade libel would be a possibility depending on the particular facts. (The post points out that materiality would be an issue in Europe, as it would be here too--the ASA evaluated whether the claim that a hotel provided complimentary toiletries was misleading, which is maybe not the most significant of claims.)