Basically, anything the dominant decides is a punishable offense. It could be tardiness, profanity, failure to complete a task, disobedience or disrespect.
Again, it's up to the dominant. There are some who are very strict, and there are others who are more easygoing.
There's a difference between play and punishment, although some of the methods may overlap. I don't agree that things you love to do shouldn't be used as punishment. I love spankings. However, there's a big difference in a spanking for punishment and spanking for pleasure. Daddy loves to spank me, but he doesn't need to invent reasons to do it. He can do it at any time and for no reason.
That's why the dominant has to be clear about the infraction that occurred and what he's going to do about it. A dominant never spanks or whips while angry since he must always be in control. A punishment need not happen immediately while emotions are high, so he could send her away until such a time as he has decided what to do and has regained composure.
I certainly can't speak for everyone, but in my experience, it's not the case. There might be heated conversation, but I know I wouldn't be permitted to raise my voice or walk away while being spoken to. A level of respect should be maintained at all times by both parties. However, it's possible for tempers to flare on either side as we are all still just human. When that happens, it's best to stop talking and separate until everyone is calm.
It's totally subjective. The dominant has to decide whether the infraction was done willfully or accidentally. Another factor might be whether or not the instructions were understood. The punishment may be more harsh for a repeated offense than for the first time.
Not if he wants to continue the relationship. A hard limit is a deal breaker. For instance, if a submissive lists golden showers as a hard limit, it means she won't do it under any circumstances. If a dominant punishes her by pissing on her, the game is over. He has just destroyed any trust and respect she had for him.