I find no problem with lying in almost any situation. In the end, it is all about Machiavellian ideology. The end justifies the means, really.
Some would counter by saying, "well, turn the tables...what if someone were lying to you?" I'd say that it is not my place to analyze, rationalize, or question the motives and intents of others. How they interact with me, yes, is a factor; but it is not really something I'd be able to help and therefore I cannot hold a true opinion on that.
As for your situations,
Example A- Why would I be looking at my mother's ass? In any event, I'd lie to her because she's fishing for compliments and wants to be told what she wants to hear, like most people. She cannot be hurt by the lie (only a valid point in the event of emotional connection with the person you're lying to...otherwise it really doesn't matter), and it'd benefit me if she were happy.
Example B- I'd lie for the man. It's not my place to, essentially, decide this man's fate. Being in that position, I'd lie because he is helping his family. Since I am simply an outside element in the situation, with nothing to gain nor lose, I can focus primarily on the man's situation and what he can gain or lose based on my honesty or dishonesty.