TT #784 · Parashas Ki Seitzei · Seventh Aliyah · Passuk 25:16
For all who do these things, all who do injustice, are an abomination to the Eternal your God.
Torah Temimah points to Bava Batra 89a.
TT lemma: כָּל עֹשֵׂה עָוֶל.
מִכָּאן אָמְרוּ: אֵין מְעָרְבִין פֵּרוֹת בְּפֵרוֹת אֲפִלּוּ חֲדָשִׁים בִּישָׁנִים וַאֲפִלּוּ סְאָה בְּדִינָר.
English: From here they said: One may not mix produce with produce, even new with old, and even a se’ah for a dinar.
On the daf / in context: Any form of deception in merchandise, even without monetary loss to the buyer, is included in “doing injustice.”
Derash extending the prohibition to all forms of commercial deception.
Mixing different grades or ages of produce (or any similar deception) is forbidden as a form of injustice.