Again on 'Would'.

Hello,

I'm back to my favourite topic; or, shall I say, my personal nightmare! At some point, in a future far, far away, I will understand how 'would' works. Seen it I have!

Here are three sentences I have heard on TV in the last few weeks. If you could help me understand why a would-construction is used, I would really appreciate it.

[I'm realizing upon re-reading that this has come out a little too long. I can make it into three separate threads if you prefer.]

a) If I would have turned him down, he would have gotten somebody else to do it.
(A hitman is talking about a job he's just been hired for; one that he probably should not have accepted).

b) If it would help you to forget, I could hit you in the head with this candlestick.

c) [Lawyer] - It's a big thing for a woman like her to lie to a lawyer.
[Man accused of murder] - They would have bribed her, or frightened her.
('They' refers to people who are believed to have threatened the woman into changing her testimony).

Allow me to elaborate a little.

a) Why doesn't it simply say If I had turned him down, [...]? What is the extra information provided by 'would'?

In trying to answer my own question, the thought occurred to me that perhaps I should start thinking of 'would' in terms of willingness.
There's a use of "will/would" - Why won't you talk to me. Or, I asked her but she wouldn't tell me. - that normally translates into my language as the verb "volere"; which in turn is usually translated as want.
So, I'm wondering, is sentence a) close in meaning to Even if I had been willing to turn him down, [...]?

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b) If there was no 'If' at the beginning, things would be simple. I would have a shift from I can hit you in the head, it will help you to forget to I could hit you in the head, it would help you to forget.
Can I actually say I can hit you in the head, if it will help you to forget?
I don't understand the presence of 'will/would' here. I think I understand from the context that this means if it had the effect of. But why 'would'? Is this another meaning of "will/would"?

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c) I'm not sure I can explain this. Although I probably have a translation for it. Is this close in meaning to They must have bribed her, [...]? If so, in my language we would say They will have bribed her.
If this comparison is acceptable, I would have only to add that in English the Past tense is used for imaginary situations - the person speaking is not in a position to know for a fact that she's been bribed, or threatened. He's imagining the most likely scenario that would account for her change of testimony - and I could obtain they would have bribed her, [...].

It's a little convoluted, but it's the best I could come up with.

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Thank you for your invaluable help.
H.