I see life as a kind of dance between Yin and Yang. What is good for you, may be bad for me at the same time. And what is good for me may well be bad for you. Yet in the end, it all balances out.
Many ancient cultures divided their experience of life and each other up in a similar way. The Eskimos imagined people as either fish people, or bird people. Oriented to the sky or to the water. Each with a different set of stories and characteristics and favored images. They couldn't tell which of these people they were, because it changed according to situation. For example, if you and I met, we might discover that you are a bird to my fish. But when you meet someone else, you might find that in that relationship, you are a fish and so are they. And the same happens between whole villages. It's just the Eskimo version of Yin and Yang.
I guess the point is that "good" is not an absolute. It's relative. "Good" to me is what's good FOR me. Good to you is what's good FOR you. And this makes good relative to the one who's assessing it. And even then it can change with time and wisdom. For example, I can think of instances in my life when something really "bad" happened to me, that later I realized to be a great blessing in disguise. So sometimes, even I don't know what's good or bad for me.
So the motives of others, and mine, too, just aren't that important, I don't think. I should try and be mindful of my own, but I don't think it's wise to put too much energy into guessing at the motives of others. "Good" is it's own value, regardless of how it comes to us.
If I'm a drunk and you buy me a drink, it's a good thing to me, even though it's not a good thing for me. And you may be doing a bad thing over-all even though I'm very grateful for it. These things get very tricky. There are no absolute or easy answers.