Many of us are caught out this way.
My late husband and I went down south to visit his son and DIL. Given my DH's disabilities, we didn't stay with them but booked accessible accommodation.
We did have a home-cooked meal at DSS's.
DH asked DSS to suggest a restaurant where DH would treat us all to a meal. It turned out to be quite an expensive place...
I was the designated driver, so not drinking. DH sent me up to the bar/till with his card (I had a POA card for him).
Just as I got there, I saw DSS getting to the bar just before me. "Aw, that's lovely. He's treating his dad," I thought.
Nope. He was ordering yet another very expensive bottle of wine (without checking with his dad, I might add).
I can't remember what the bill was, but I remember that the barman/waiter was clearly very worried since it was obvious that the person paying was the one visibly disabled elderly gentleman in the party.
I reassured the barman and paid plus tipped him, but inwardly I was seething. The kindest explanation that I can think of is that DSS was a journalist and far too used to putting food and drink on an expenses account.
Before anyone asks, DH and I normally split bills but latterly he took on all expenses related to his kids since he realised that I was being expected to give but not to receive all the time.