I charge $10 a head to cover cost of wine. She walked out without paying, I didn't say anything, I think the other couple reminded her in the elevator and she came back and left $20. I told her it was only $10 and she said "It's worth $20".
That was a fun group, they stayed from 6 until nearly 9. One of them is a retired MD who is quite interesting, and arthopod, or "organic mechanic" as he called it.