Apologies are also an art

It is not easy to adequately apologise to a customer, if you have caused an inconvenience.
Years ago I was aboard the Eugenio Costa and, off the coast of the infamous (and historic) Cape Matapan, the ship’s engines broke down and were idle for two days, in the middle of the sea; this caused a change of itinerary, and the stop at Varna (Bulgaria, Black Sea), where I presumably will never again have the opportunity to go, was cancelled.
In order to indemnify passengers for the inconvenience caused, Costa provided a discount voucher on a future cruise: ridiculously insufficient!
At a nice restaurant in Bratislava, my wife and myself ordered a goulash and a deer cutlet; after almost an hour’s wait, the cutlet was served piping hot, while the goulash was barely lukewarm (for technical reasons easy to guess); after I complained, the owner, who was waiting on us, had the goulash warmed up and then disappeared from our sight except to present the bill; we did not even have a chance to order a dessert! He was probably ashamed of the poor service, but in so doing he created a sense of discomfort. It would have sufficed to offer a liqueur with a smile. Shy.
In the mountains, during Christmas dinner at a history-rich restaurant, seated in a small veranda overlooking the snow-capped wood. Beautiful! We ordered the Christmas menu and some excellent wine to celebrate the occasion. Half way through the meal, the wine had not yet been served; I reminded the waitress, who assured us that the wine would be brought immediately and, by way of apology, asked me if I would like a glass of bubbly. Hard to think that midway through a meal, in place of a red wine, I might appreciate a glass of champagne. Kind, but inappropriate.
I was in Berlin for the ITB, sitting in a beer place, waiting to be served the beer I had ordered. Out of the corner of my eye, I observed the glass on the counter, where the think foam was dying down. Finally the waitress approached to retrieve it and, seeing that the foam had gone down, insisted for the barman to top it up to the rim (the way it should be). The waitress might have not cared and might have served the beer as it was, sparing herself the trouble of discussing with her colleague, but I would not have enjoyed my beer to the best.
What is, then, the correct way to apologise? As in the case of the beer, by placing yourself in the condition of not having to say your are sorry …