Chofetz Chaim Daily 23 Elul 9:13 If the buyer will cause the seller any unrightful loss, it is asur to tell him that he was overcharged. The Chofetz Chaim bemoans the common practice of people degrading other’s purchases. If the buyer has no claim min hadin, there is no toeles. Most often the sayer isn’t educated enough to be able to determine the correct current value of the item!
Chofetz Chaim Daily 24 Elul 9:14 If someone suspects YOU of wronging him, and you know who really did it, you may not tell (unless all conditions met). You may say it wasn’t me. 9:15 Ex: You put something aside for buyer. Ploni comes, pays, and takes the item. You do not protest. When original buyer returns with $, you may not tell him its ploni’s fault. It is asur to say ploni’s name, even if you accept blame. All hilchos LH do not apply to people who are public kofrim.
Chofetz Chaim Daily 25 Elul In a case of potential partnership, one should not assume that ploni’s poor financial situation makes him a bad candidate for a partnership. BUT in such a scenario, where you may not want him as your partner, you shouldn’t recommend him either. That may be bad advice