I'm very late to this part of the discussion... but I just realized that I should object to the use of "sharing" as a way of describing a site like airbnb.

I'm a little irritated with myself, because I actually referred to it as a sharing site in an earlier comment.

While there can be some ambiguity around the word "sharing", this one is not a tough call. Airbnb is a commerce site, it absolutely is not a sharing site.