I assume they couldn't be honest because it would've violated Craiglist's Terms of Use, namely:
You agree not to post, email, or otherwise make available Content:
k) that constitutes or contains "affiliate marketing," "link referral code," "junk mail," "spam," "chain letters," "pyramid schemes," or unsolicited commercial advertisement;
l) that constitutes or contains any form of advertising or solicitation if: posted in areas of the craigslist sites which are not designated for such purposes; or emailed to craigslist users who have not indicated in writing that
it is ok to contact them about other services, products or commercial interests.
m) that includes links to commercial services or web sites, except as allowed in "services";
I wonder if Craigslist could legitimately sue Airbnb.