And on the topic of soda, someone upthread had a good point, I thought, about how they would feel comfortable helping themselves to a can of soda in someone's fridge (under the general "make yourself at home" banner), if the soda was a very common thing like Coke, Pepsi, Sprite, etc.; but they would hesitate to help themselves to something more exotic-looking, like a brand of soda they didn't recognize (there's a lot of specialty ones, kind of like microbrews for beer I think).
In other words, they would feel comfortable using something they absolutely knew
was common and inexpensive, but less comfortable using something that they couldn't immediately place or that seemed more rarefied. It seems like the couple in the OP (lo those many pages ago) had a reasonable expectation of being able to drink some
of their host's wine, but I feel like they really erred by not sticking to kinds they knew or looking them up first. It's like they looked at the bottle and said, "Nope, never heard of this one, by default it must be something common and cheap, let's drink it."
Okay, this is not a floggable sin in life or anything
but the assumption of "I don't know what this is, I'll use it" instead of "I don't know what this is, I'll leave it alone" would make me
uncomfortable about our relative boundaries, so I probably wouldn't put them in a situation again where they could cross my boundaries. Though, I think I would still be friends with them, because they showed themselves to be honest and to have good intentions by replacing (mostly) the wine.