At my tables, I have asked the players if they wish to play "touch move", or "take your fingers off move", or even "take back moves"... to use chess analogies. That way the players can choose the difficulty they wish to play at. It seems t cut down on arguments letting the table rule on how serious mistakes could be. Retconning spells falls a tad outside these guidelines (it falls closes to "take back moves") but, hey, they are guidelines!