Avraham: Rabbi Rich, Yitzi asked me for m'chillah, but I don't feel like giving it to him
RRW: Aren't we taught not to be an achzar and to extend m'chillah when asked? ....
Av: I know, but, I still feel something's not right..
RRW: Is he a repeat offender?
Av: No - it's not that
RRW: Well Av,. What is it?
Av: I guess Yitzi did say that he's sorry that he confused me with someone else BUT...he said a BUT in his apology
RRW: ??? Continue
Av: He didn't admit he was completely wrong, he passed the buck and partially blamed me anyway
RRW: Was he right?
Av: Hard to tell. What he blamed me for was something unintentional, hardly worth commenting upon. He seemed to be using blame to rationalize the behaviour that he was expressing remorse over.
Mussar: when apologizing don't qualify it with "BUTS"
If you do need to express a reservation or caveat try using a separate conversation or email to point out that issue. Otherwise, the BUT may be m'vateil the haratah.