There's a quiet litmus test: does the bathroom window open? It's a small thing — but it tells you a lot about how a place thinks about its guests. Air-conditioning is one thing, but the ability to hear the rain, or smell the sea at 6 a.m., is something else.
Other tests: is the kettle full when you arrive? Does the staff use your name by the second morning? Is the breakfast menu designed for guests, or for the chef's Instagram?