Seems to me that most of those small bottles have some sort of seal that would clearly show it had been opened before you handle it. And there is a terrible liability potential if s property engaged in refilling those bottles and either made a mistake with the contents or some of the contents were tampered with.

We stay primarily at full-service Marriott properties. Until a few years ago it was common for any opened small bottles to be discarded by housekeeping each day and replaced with new ones. Now the opened bottles are left for the guest to continue using, but a fresh unopened bottle is always available when needed. That encourages the guests to use up each bottle - and saves Marriott some money too.