The map in hotels.com does a good job of clustering. For example, searching for hotels in a high density area like NYC. Airbnb, conversely, does not seem to have any clustering. Properties vanish and reappear at various zoom levels.

agreed re: hotels.com - what I see them doing well:

- don't cluster aggressively ie break out the clusters earlier (even if markers end up overlapping) - allow clusters and non-clusters to co-exist on the same zoom level (this is usually the case - except when maps are implemented to have "cluster only" levels and "point only" levels) - show immediately useful information in the point marker (the price!)