Banquo in those words means that many times the "bad guys" do not have to lie, cheat or hurt us physically. In the case of witches they do not lie to them but they tell half truths to Mcbeth and Banquo, this makes Mcbeth tempt to follow the predictions of the witches without thinking that there may be other truths and consequences. In the end, these half predictions lead Macbeth to its ruin.
According with the last, Banquo doesn't trust the witches because they only tell us the good and not the bad . They just give half truths.