I worry about this too. I went to a Pub and a man next to me struck up a conversation and we talked through the hour. I had to do the restroom check and I was concerned that he might have tried to pay my check, while I was in the restroom..
Thankfully, he did not but I worry, what if?
If someone pays the tab, I guess we just get the shop fee?
Or, do they throw the whole thing out?
Or, do they pay you everything, as if you had paid for dinner?
Curious...