In the first example, you should just continue playing tit-for-tat, if the other player truly "slipped" and knows you are playing tit-for-tat, he won't defect after you defect, he will continue cooperating and make you cooperate.
The whole notion of pre-commiting to a strategy is to remove the human elements like "negociation" and "excuses". You are a machine and you play accordingly. If the other player is rational, he will cooperate even after he slipped and you defected.
Hi, first post, what is a point of karma?