The way I played, was just use common sense. If you are pretty confident your opponent is skilled enough to check mate you in one or 2 moves you can just concede and resign. It is possible he may not see it, but if you are in that position it is highly probable he knows it. Congratulate them on their win. Lose with the same dignity you win with. In otherwords the Golden Rule.
Surrender vs mate
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The original question I had here was (I deleted it thinking it would disappear, but no, instead there is just a deleted comment comment): Is there a defined chess etiquette on surrendering vs playing to checkmate.