(Happy Birthday, Deb! Or was it yesterday??)
When I was a child, my sisters and I had to say “May I be excused?” before leaving the dinner table. This was to signal many things: we were finished eating; to give our parents an opportunity to review our plates; to teach us how to be civilized; to consider other people; to become accustomed to decent manners.
So, now I say to my customer, “Please may I be excused?” This is because I believe the oil painting is finished, because I am civilized, and because I am never finished until the customer is happy!