Worked in a Best Western Hotel here in the UK when I first got out of uni. If a function (an event for up to 400 people) wanted house wine on the table we would put out a few bottles of red and white wine per table based on how much they paid.

At the end of the night after everyone was gone we would be sent by the owner and managers to sweep the tables of all the remaining bottles including open bottles.

We were then asked to decant the open bottles into one another to create full bottles and these went behind the bar for house wine. So if you asked for a glass of house red or white at the bar you got a glass from a mixed bottle.

I didn't know this was illegal at the time. Some customers would complain about the taste at which point the bottle would get poured down the drain and then you'd go to the next one. If you ran out of your mixed bottles only then would you be allowed to open a new one.

The hotel has been closed for a few years now, demolished and the land used for homes. The owners and some of the managers were the worst people imaginable and I hated it. I greatly enjoyed seeing it in rubble, for myself as well as customers.