Hamlet seems to distrust R and G very strongly, whereas if I think about it I don't really know what they did wrong.
They did tell a little lie to begin with to Hamlet, regarding why they came but at the end of the day they were only doing of what they were asked from the Queen etc. and they did come clean, other than that they havn't done anything, yet Hamlet is very aggressive towards them.
He begins by almost mocking them and pretending to have misheard them "O wonderful son, that can so 'stonish a mother"
R reacts to this by trying to bring out his good side, to remind him of the friendship the once had "My lord, you once did love me"
they are very reasonable and try to ask Hamlet why he is acting in this way "Good my lord, what is your cause of distemper? "- and they continue to try and reassure him and tell them of what is causing him to act in such a way by saying that he should tell them so they can help him, "you do surely bar the door upon your own liberty if you deny your griefs to your friend."
I do not think R and G deserve the treatment they recieve from Hamlet, but I think Hamlet probably pressumes them evil, as they are associated with Claudius, but really all they did was come to ask Hamlet if he could go and see his mother.
Yet Hamlet goes on to have a huge go at them and says after asking G to play the pipe, and G refusing says "Why, look you now, how unworthy a thing you make of me! You would play upon me!" - Hamlet beleived they played him, made a fool of him.