[60a top] Mishnah: If one’s barrel of wine had water mixed in, he must not sell it in his store, unless he informs the buyers (that it is diluted). He may never sell diluted wine barrels (as a wholeseller) to other merchants, even if he informs them of its diluted states, for the store owners’ intentions may be to deceive customers [Rashi: he would be placing easy stumbling blocks in their way].
R’ Rosner quoting the Sma: Since the store owner would not have been the one who did the diluting of the wine barrels, he may justify his incorrect sales as claiming that he is just the middle man (and did not physically do anything wrong to the wine himself) [but he would have more of a guilty conscience if he would have done the ‘bad deed’ of diluting the wine].
D-E-ep Thoughts: Even if people do not do things technically wrong themselves, if they ‘hang around’ impropriety, they are likely to get pulled down. We should never purposefully put ourselves in compramising situations. The strongest people can be the weakest when overcome by the Yetzer Hara’s tricks into moments of foolishness (Heaven forbid). We must guard the souls that we are by creating strong fences and regularly checking the locks on our gates.