But, from the inside, how to you tell the difference between doing actual good for others or being an omnipotent moral busybody?

"She's the sort of woman who lives for others - you can tell the others by their hunted expression."

Having a good factual model of a person would be necessary, and perhaps sufficient, for making that judgment favourably. When moving beyond making people more equal and free in their means, the model should be significantly better than their self-model. After that, the analyst would probably value the thus observed people caring about self-determination in the territory (so no deceiving them to think they're self-determining), and act accordingly.

If people declare that analysing people well enough to know their moral values is itself being a busybody, it becomes harder. First I would note that using the internet without unusual data protection already means a (possibly begrudging) acceptance of such busybodies, up to a point. But in a more inconvenient world, consent or prevention of acute danger are as far as I would be willing to go in just a comment.

Willingness to be critiqued? Self-examination and scrupulous quantities of doubt? This seems kind of like the wrong question, actually. "Actual good" is a fuzzy concept, if it even exists at all; a benevolent tyrant cares whether or not they are fulfilling their values (which, presumably, includes "provide others with things I think are good"). The question I would ask is how you tell the difference between actually achieving the manifestation of your values and only making a big show of it; presumably it's the latter that causes the problem (or at least the problem that you care about).

Then again, this comes from a moral non-realist who doesn't see a contradiction in having a moral clause saying it's good to enforce your morality on others to some extent, so your framework's results may vary.

If someone clearly wants you to stop bothering them, then stop bothering them.