The central question for me is always: are you trying to make them do something they don't want to, that wouldn't be in their interest nor the interest of the greater good, and are you being deceptive.

Example 1: You're discussing something political. Part of that is often trying to convince someone that your opinion is right. Your believe your opinion is right, and you believe your opinion contributes to the greater good. Not manipulation.

Example 2: You're creating propaganda. You're trying to convince masses of people of something, you're putting the information together in a deceptive manner, and you're trying to further your own interests. Manipulation.

Example 3: Someone's depressed, and you're trying to get them to come on a walk with you, because you believe it would help their mental health. They don't want to, but you believe it would be in their best interest, since they're isolating themselves and it's not doing them any good. Not manipulation.

Example 4: you want to borrow someone's car. They don't initially want to lend it to you. You offer to grab groceries for them and fill up their tank. They figure that in that case, they would be OK with lending you their car. Not manipulation.

Example 5: you want to borrow someone's car. They don't want to lend it to you. You remind them of the time they accidentally broke something in your house so that they feel guilty and oblige. This was solely in your own interest. Manipulation.

Are you transparent with what your goals are. Are you giving them correct information. Are you giving them all important information and not lying by omission.

when you want them do something at thier expense, like convincing them to drive you everywhere or live rentfree at thier property in indefinitely, or isolating a SO/ or anyone(extreme) so they are more dependent on you, usually these forms require deception as well, or emotional guilt tripping.

Convincing someone is an attempt to manipulate them into changing their behaviour.

Giving your reasoning seems to me like you are attempting to educate. Nothing wrong with that as long as people are asking for your opinion.

(edit: sent mid sentence on accident)

Every interaction between humans is manipulation. Every single one - including not saying something.

With that framing: Your question sounds to me about the negative connotation ("being manipulative") - and for me that's simple: sincerity and intent.

Before coming to your last paragraph I go with an extreme as example, abuse, because it's so black and white:

I try to convince you to leave your abusive partner. I try to alter your whole life - because I'm convinced that it's the right thing for you.

If I tell you the same thing to get off with your current partner or to harm you, it's manipulative.

Now for your example: For me it's the foundation of our human interaction to bridge gaps - social, communicative, personal.

We always have incomplete data sets (if only about the perception, interpretation and knowledge of the other people around us). We're always in an interpretation gap.

Now if you withhold information other humans are worse off, even ignoring what other people call "the objective truth": they don't know where you stand, what your reasoning is and what values you hold. All of this shines through even when just saying, as a random example, "I don't want bacon" - this can be health, religion, mood, taste and a miryad of other things related that will help other people connect (or avoid) you.

In short: don't break other people's heads! Every human needs to evaluate information they get - as long as you're sincere and don't try to evoke a behavior that you know is against the best of your surrounding you wouldn't fall into "manipulative" in my book.

When they say no, and that’s final/to drop it, and you still try to convince them.

I would also like to hear other people persoective on that.

Because obvious answer would be to convince them on subconscious level instead by directly convincind them.

But a mere praise can often change someone interest and even values.

It gets even trickier if we are talking about raising a kid. You actually want them to adopt your values etc... You are supposed to praise the behaviour you want. Especially if they are to small to understand reasoning. And you fully understand you are completely shapping their personality on a level they do not understand.

So I do not know. Maybe all of that is manipulation but not all manipulation is bad?