I thought I should-prob share the notion of using "should-prob." It's obviously only good for non-formal situations, but it's better than nothing.
To elaborate, there seems to be a very wide band between "should" and "can" where a person has an educated opinion, but acknowledges it as opinion (and therefor fallible).
Telling a person what they should do gives the impression that there is a right and wrong, and that you know which is which. Telling a person what they can do implies there is no right and wrong, and you don't have an opinion.
Between these two can be imagined a situation where there is a right and wrong and you have an opinion but do not know what to do. A suggestion if you will.
What's strange is that of these three scenarios, the missing one seems the most common. Anyone who knows what's right and wrong is probably misguided, and notion of having no opinion on a subject is probably a lie.
Anyways, for now I'm using should-prob until something better comes up.