To be fair, I think that part of the reason he's salty at AirBNB is because 'David' was a verified user and vouched for by AirBNB. It seems like there was a level of endorsement from AirBNB to indicate that 'David' was on the level, and that turned out to not be the case at all. So it's less like buying something on craigslist, having the deal fall through, and claiming that it's the fault of craigslist; it's more like buying something from Amazon through a third party and then complaining to Amazon that the item wasn't advertised honestly. While I don't buy a lot of stuff from Amazon third party sellers, I believe Amazon does offer some level of protection for the consumer.
Honestly, I don't know; my first experience with AirBNB was waking up one morning to discover that somebody had used my email account to list their apartment for renting, and I got a whole bunch of emails from people who were super interested in it. I got control of the airbnb account by resetting the password, changed all the credentials, and contacted airbnb to let them know that a) they should probably not start listing apartments for rent without confirming that the lister controls the contact information and b) I was horrified, but the experience kind of put me off them as a service. Stories like this don't help either.