可不是吗 / 可不是 / 可不 (+ ,[detail])
可不是吗 answers someone's remark and agrees with it warmly. It looks like a negative question – "isn't it?" – but it means yes. The shorter 可不是 and 可不 mean the same and are more casual.
The reply often goes on to add a detail of its own, as in the second example.
可不是吗 agrees with an opinion or an observation. It doesn't answer a yes-no question; for that, repeat the verb.
不是…吗 with something between is a different pattern: the speaker reminds the listener of a fact, 你不是说要来吗 "didn't you say you'd come?". 可不是吗 never has anything in the middle.