How Likely? - Modals

It seems (from the given circumstantial details) as though it is almost certain that someone is at home. None of the other Answers is as strong and confident, though No.4 is possible if we are being very cautious ... and not making assumptions, nor leaping to conclusions!

This suggests clearly that you think it more likely than not that your trip there will be wasted. You are not literally making a bet (though you could even say 'I'll bet' or 'I'd bet') ... but you are expressing your opinion that you are certain enough that your money would be safe if you did!

Any of these will convey the sense, but there are subtle differences in how they do it.
Answer 1 simply refuses to accept any possibility of a fault: '100% of brand-new machines should do their job without problem.'
Answer 2 suggests there are no circumstances or means in which a fault could have arisen, if the machine was checked at the factory and has been installed and started in accordance with the instructions.
Answer 3 appears to suggest that nobody gave the machine permission to malfunction. This isn't what we would normally say.
Answer 4 expresses the idea that the machine has 'failed in its duty' and 'not done what it was supposed to'; in an ideal world, such things ought never to happen!

Answer 2 is the standard phrase (you may have heard the tennis champion John McEnroe, challenging the court officials at Wimbledon with it, back in about 1980!). It implies that there can be no other explanation for what the official said, other than that he was not being serious.

This is the 'might well' phrase and it means 'It makes no difference whether you are a Director or not; the rules apply just as much to you as to anyone else'.

Only Answer 1 is clearly wrong here; 2 and 4 express various 'shades' of possibility. But only No.3 picks up the use of the 'theoretical' Past Tense ('If you came, I could ... ') ~ although as a whole, this refers to the possible future.

'One thing may be true, but another thing does not automatically follow from it.'

This sounds like a sincere acceptance of an open invitation, but there is still the equal possibility that it 'might' never happen ('We might never 'get round to it' ' .)

'Could' is even better than 'can' (Answer 1) here ~ because, by using the Conditional, it suggests there is even less chance of any other explanation.

Of the first three Answers, this appears to hold the strongest likelihood.
As this is Reported Speech, 'will' (Answer 4) is not quite right, even though it may have been among the actual words he said.