על מכרם בכסף צדיק ואביון בעבור נעלים - (עמוס ב-ו)
In the Haftorah, Amos HaNavi reminds Klal Yisroel of the infamous sale of Yosef HaTzadik at the hands of his brothers, and how it was done for such a paltry sum, a pair of shoes. However, it seems that the error was in the sale - insinuating that had Yosef been merely given away to slavery for free it may not have been so bad.
R’ Shloime Kluger zt”l (Chochmas HaTorah) explains that often when a person does something wrong, he tends to rationalize his misdeed. He may even “outsmart the system” and find a technicality to make it as though his action was not in fact an aveira. While he may escape judgment on this world, Hashem nevertheless knows what he did, and his punishment will come.
In the parsha we see that Yehuda exclaimed “What do we gain by killing our brother and covering up his blood? Come, let us sell him to the Yishmaelim, but let us not do away with him ourselves.” But they already decided not to kill Yosef - why did Yehuda reiterate it? The answer is that the brothers wanted to be as clean as possible and so they arranged for the Midianites to haul Yosef up from the pit and then sell him to the Yishmaelim. That means that technically, they had nothing to do with it. However, they made one mistake. By accepting money in exchange for Yosef, the brothers became implicated, placing themselves on the hook for not only the sale, but for all the suffering Yosef endured in the years he was separated from his family in Egypt.