Musar for Arakhin 31:4

Even more so, should he take care not to speak to a shopkeeper about other shopkeepers or with any tradesman about his fellow tradesman. For, in all probability, one tradesman does not love the other and he is very likely to come through this to lashon hara. And if one knows that the first harbors hatred against the other, he should certainly not speak to him about the other. And, it goes without saying that he should not praise one to the other, which is certainly forbidden, as Chazal have said (Arachin 16a): "Let one not speak in praise of his friend, for from praising him he will come to demeaning him," all of which I have explained in Chafetz Chaim, Part One, Principle IX. And it is also highly advisable to avoid with him even speech in general, which is not in the class of demeaning or praising. For in his hatred of the other, he is highly likely to draw the speech in another direction, which will make it easier for him to shoot the arrows of his mouth against him.