Re: how many back talk would you take?
If the person doesn't want to follow the sensei then it's a problem.
If the correction is coming from a sempai or a kohai and the partner doesn't listen, it shouldn't be your problem. People in the dojo always have the urge to teach something but regardless how good our intentions are with imparting our knowledge, no matter how "good" we are or how we think how good we are, we can't force somebody to accept the information we give them. It is their journey.
I also observe in some occasions that when we teach, we talk too much. The more we talk, no matter how great and superb the idea/principle is, the lesser we train. Aikido is about doing and about feeling. You get good at aikido when you train a lot IMHO, not when you talk a lot. That is why I understand in some dojos talking is forbidden during practice.
Also, the partners learning accelerates from the ideas he himself discovers not the verbal things imparted to him. Once a person discovers by himself something new, it leaves an indelible mark in his brain and these things he discovers by himself mostly likely won't be forgotten. A verbal correction even by a sempai or even sensei will pass through one ear and out the next.
That is why when I have the urge to correct my partner, I zip my mouth and let them do the technique even if its wrong. Though I give them some resistance where there are openings. It will take a long time (or very very long time) for them to get it but you will find everything will turn out OK in the end.
If they are sincere in their training, they will get good. If they don't get good, ultimately they will get good later or they will stop training eventually, so why worry about the outcome?
Being argumentative though is a different story.