There's been a lot of discussion about how many non-alcoholic drinks you are entitled to in Business Class. I've experienced both "just one" and multiple about the same number of times.
But this time I had a unique situation, where I happened to get the same guy on the Maine Downeaster in both directions a day apart. On the trip up, he gave me two comped diet sodas. On the way south, he charged me for the second one. He was a really nice guy, and I asked him about it. He said that at least on the Downeaster, they have to account exactly for every comped drink, as part of the inventory. He is only allowed to give out exactly one comped drink per seat. He said that on my trip north, there were many empty seats, so he had plenty of extra, but on the way back, business class was full. I asked him what happened if the same seat was occupied by two people with different trip segments, and he said he had to write a note explaining why he had used more than his comps. He said they were very strict about it, and his supervisor would check his report and exact inventory on every trip. I'm surprised they don't check to see how many business class seats were purchased
.
Again, he was quite pleasant and seemed knowledgeable, so I don't see why he would be making it up. At least on the Downeaster website FAQ, they say "and a non-alcoholic beverage served to your seat".