We told them to "make themselves at home," but never stated "feel free to drink our wine!" But, if they had drank ANY other bottle we owned we really wouldn't care. But like I said, it was wrapped in tissue paper (unlike all the other bottles) so it was clearly special.
This is a work friend of my husband's, and due to work circumstances he really wouldn't feel comfortable asking for payment. Obviously, they'll never cat-sit for us again. Just wondered if I should day something, like, "Just so you know, you drank a really expensive bottle of wine!" or something like that...
Honestly, me? I think I would just drop the issue and let it go. I would probably even go so far as to get them a small gift certificate to Starbucks as a "thank you," and not do anything expensive like dinner, which I would normally do, and that's only because of the work rel@tionship and trying not to create bad vibes with the work environment. That's just me, though you have gotten some great suggestions.
As someone who has house-sat many times, there's no way I would go into anything that wasn't expressed to me is free-for-all, and in these cases, these people have had perishables in the fridge that they're happy to see used, and even beer. "Help yourself to anything in the fridge." A specially wrapped bottle of wine stuffed in the back? That's a no-brainer, "no-touchey" in my mind, and I'm wondering what these people were thinking. Regardless of the implied free-feed situation that may have been implied, that's not an open invitation to clean people out of house and home. I think they crossed a bit of a line going after more than one bottle, let alone the fancy one stuffed in the back. After house-sitting, if I use the last of the coffee, I replace the coffee. Grab some milk, so they have it when they return and can deal with shopping later. Drank all the beer, replace the six-pack. Run the dishwasher, wash the sheets and towels, and if you use up all their laundry soap, replace that too. Back in the college days, house sitting was a huge major blessing that came with use of the laundry...woo-hoo! I was also offered having friends over. I didn't take that to mean I could have a big ol' party.
Give an inch, take a mile...no, no, no!
At the end of the day, live and learn. Be clear in the future - you can help yourself to anything but this bottle of wine. Leave a note on it. You may have your boyfriend/best friend over, but no other guests. That sort of thing.