Learn English – Polite way to ask

You are right about context and intonation playing a very important role in these sentences.

If you ask a taxi driver to hurry because you are in hurry by saying "Will you hurry?" you are actually asking the driver's willingness and will hurt his/her feeling.

If you are stuck in traffic, asking the driver if he will hurry may indeed hurt their feelings, since it seems obvious that their willingness to hurry is not questioned by the fact that they are simply unable to hurry. (Albeit that some drivers have very original ways to enable them to hurry even in very busy traffic, and that their willingness to do so may increase after the promise of an extra financial reward...)

Indeed, the use of "will" normally inquires directly about a person's willingness to perform a task, and we normally assume that the person is able to do so. Asking them if they are willing when they are obviously unable might be insulting. On the other hand, you could use "would" for a hypothetical situation: "If you knew Spanish, would you help me with my homework?"

"Could you ~?" is usually more polite than "Can you ~?" but only when you ask for help "Can you help me?" is more considerate than "Could you help me?" because when the answer is no the person feels more easier to say no.

"Could" is indeed usually more polite indeed. Where "can" simply asks whether the person is capable of doing something (and implying that you would appreciate they did it!), when you use "could", you are implying that they have to also have a willingness to do it.

So indeed "could you provide an example?" is more polite than "can you provide an example?", but can is the correct form to use when you are genuinely wondering if the person is able to do something:

Can you come to the dinner party this evening? => Are you able to make it, or have you another appointment?
Could you come to the dinner party this evening? => It would be much appreciated if you would come.

"Would you mind ~?" is not polite way of asking but it's rather cynical.

It is actually a very polite way of asking. "Would you mind giving me a hand?" is more polite than any of the previous forms.
However, exactly because is is so polite, it is often too polite in most circumstances! And because of that, it can be very effectively used in a cynical way, in the same way we can use formal forms of address or other (extremely) formal language.

As such, nobody will think of cynicism if a lady asks a stranger:

Would you mind helping me cross the street?

But if I address a friend of mine in this way:

Miss Jones, my dearest, smartest friend, would you mind terribly if I were to decline your kind invitation to your extremely interesting lecture on the history of quilting in 1970's rural Northumbria?

I am quite sure she, and anyone who heard it, would understand that I might be a bit cynical about the interest in the subject as well as my actual appreciation of the invitation - and most importantly, it would be understood I am not actually inquiring whether she would mind my rejection, I am assuming my rejecting should come as no surprise to her!

Not sure if this is exactly what you want to understand. I didn't read through the other posts. Solely going by the examples you gave:

There is still a condition that needs to be met in both instances.

First example, it is uncertain that the guy whose fingerprints they found is the actual burglar. He hasn't been formally convicted of the crime. Therefore, he is still only a suspect until further investigation and prosecution.

"Why did he steal the money?" Means that he did steal it but they want to know the reason.

"Why would he have stolen the money?" Means they want to know the reason this person (provided he is the culprit) wanted to steal it (possibly to use this as evidence in a prosecution.)

Second example, I can't pinpoint because I don't recall this passage but it seems that it's possible someone else investigated and B didn't get the opportunity or something to this same effect. B somehow didn't meet a certain condition in order to actually investigate but you can't make the claim that he actually investigated.

Your sentences are grammatically correct but they don't fit because they conclude that something has happened. The thing is, we don't know for a fact that it did happen.

Hope this helps some.

EDIT: I just read the other posts. Aside from what has already been stated in the other post about 'expression of disbelief'. It is also a matter of intonation, emphasis and context.

Consider this:

/Why would he steal my money?/ - uncertain if he is the culprit

/Why would HE steal MY money?/ - uncertain and stressing ownership

/WHY would HE steal my money?/ - disbelief that 'he' is the culprit

Although all three are written the same way, from a written dialog it would need to be deciphered by context. In a spoken dialog, it would be deciphered by tone and emphasis (and context.)