Reputable hotels, like mine, set the hosts down and give them a consumption sheet showing the amount of liquor, beer and wine that is stocked at the beginning for the function.
We then show the end of night inventory to them and compute the consumption based on that. All functions are separate and have separate liquor “cages” to control the inventory.
If something needs to be added (ran out of a beer brand for example) we have the hosts sign and approve a transfer sheet to show the added booze.
I am not suggesting that all facilities are dishonest, but lets not be naive here, its very easy to fraud if one desires too.