[Spivak]

> tourists that will use their service over an over again in a different city

This is the part that I don't think follows. Why would they? There are a million different travel sites and people do their homework. There's nothing preventing people from using different booking sites for each trip. I see an advantage in having a large portfolio of hosts but I don't think they will ever be at the point of charging a premium because they have lock-in.