I had the experience a few years ago on holiday, but it could happen at a restaurant nearer home.
I ordered wine with my/our meal and I noticed the bottle was open when the waiter brought it to the table.The cork was out but just pushed in a short way, enough for him to pull out with his hand. He proceeded to do the usual, pour a small amount into my glass for approval. I said I dont want that bottle bring another.
When asked what I did not like about the wine I said, I dont know whats happened before hand, you could have made up a bottle with dregs from other customers bottles that have been left.
With the increasing use of screw caps these days could this practice go unnoticed.
I used to work for a corporates events company that also catered weddings.
I was pretty disgusted when the wine for the tables, that were bought and paid for by the bride and groom, was re-bottled and re-sold to the wedding party, including the bride. It's embarrassing charging a bride £4 for a glass of wine that she'd already paid for...