Incidentally, I was involved in somewhat similar case with a plumber (someone I worked alongside with on occasion when I was in the trades) who did various small jobs at our place. We did not receive a bill for a little over a month and I called to let him know (motivated in part because I knew him?). He said the work was “gratis” (his word) owing to the fact that one of my brothers, a general contractor in town, had sub-contracted an awful lot of work to him and this was one way to show his appreciation.

And recently I bought a few books and an expensive calendar (reproductions of Tibetan Buddhist art) at a small religiously-oriented bookstore and realized when I got home and looked at the receipt that we were not billed for the calendar (I usually don’t look at my receipts but this one was rather large and thus easy on my eyes). I called to let them know (fear of divine retribution or bad karma?) and said I would be sending a check to pay for the calendar. Later my wife said something like, “well, if that was some big department store, I don’t think I would have called them, as they don’t need the few extra dollars.” Our subsequent discussion hinged on the question of whether or not that was a relevant difference.