Short answer. Article 473 of the Civil Code penalizes the person who mixed things in bad faith: they lose their own share of the mixture entirely and must also indemnify you for the damage the mixing caused, on top of whatever your rights over the good-faith mixture would otherwise have been under the preceding provision.
What the law says
If the one who caused the mixture or confusion acted in bad faith, he shall lose the thing belonging to him thus mixed or confused, besides being obliged to pay indemnity for the damages caused to the owner of the other thing with which his own was mixed.
Civil Code, Article 473 — Mixture by One Owner. Read the full provision →
Bad faith changes the outcome entirely
Article 473 draws a sharp line based on the state of mind of the person who did the mixing. Where that person acted in bad faith, he shall lose the thing belonging to him thus mixed or confused. Ordinarily, mixing two owners' grain or produce would raise a question of dividing the resulting mixture between them — bad faith removes that question for the wrongdoer's share. He does not get a portion of the mixture back; his contribution is forfeited outright.
Losing the mixed portion is not the only consequence
The article adds a second consequence on top of the forfeiture: the bad-faith party is obliged to pay indemnity for the damages caused to the owner of the other thing with which his own was mixed. So this is not simply a forfeiture-for-forfeiture exchange. You are entitled both to the outcome that the wrongdoer's own share is lost, and separately to compensation for whatever damage the mixing actually caused you — the two remedies stack rather than substitute for each other.
This is the exception to the good-faith rule
Article 473 is explicitly framed against a baseline for mixtures made in good faith, where the rights of the owners are worked out by the provisions that immediately precede this one. What this article does is carve out the bad-faith scenario as a distinct, harsher regime — it exists specifically because the ordinary good-faith sharing rule would let a deliberate wrongdoer walk away with a portion of a mixture he intentionally created to your detriment, and the law refuses to let that happen.
What bad faith needs to be shown
Because the whole outcome here turns on bad faith rather than an innocent mixing, focus on what shows the mixing was deliberate and knowing — how the grain or produce came to be combined, whether the other party had access to and control over both stocks, and anything suggesting the mixing was not accidental. The stronger that evidence, the more clearly your situation falls under this article rather than the ordinary good-faith rule it displaces.