When I feel someone is thinking this way ("true reason is laziness"), I instinctively react in an unpleasant way. I've been using a phrase "you treat me with less respect you'd treat a stranger" to remind them that empathy goes both ways, and I'm not their servant but independent human being.
I.e. if in the way you ask you show you're expecting them to comply, you're doing it wrong. Show respect to people's need for autonomy, and they'll be more willing to help you out.
I have a friend like this and, while we get along great most of the time, he is always interrogating people who say no to him and you can just tell he's assuming 'the true reason is laziness'.
People make complex decisions and they shouldn't always have to explain why. Especially with someone you trust.