Short answer. Because the seller genuinely did not know of the hidden defect, the seller only has to return the price you paid with interest on it, and reimburse the contract expenses you actually paid — a narrower recovery than a knowing seller would owe, and without any additional damages.
What the law says
If he was not aware of them, he shall only return the price and interest thereon, and reimburse the expenses of the contract which the vendee might have paid.
Civil Code, Article 1568 — Loss From Hidden Defects. Read the full provision →
The rule for a genuinely unaware seller
Where the thing you bought is lost as a result of a hidden fault, and the seller had no idea the fault existed at the time of sale, the law limits what you can recover to three items: the price you paid, interest on that price, and reimbursement of the expenses of the contract that you actually paid. Nothing more is owed to you under this specific provision when the seller's ignorance was genuine.
No damages where the seller did not know
This is the key difference from a seller who knew of the defect: an unaware seller does not owe damages on top of the price and expenses. The law treats honest ignorance more leniently than concealment or actual knowledge, on the reasoning that a seller cannot be expected to disclose a defect it had no way of knowing about. The remedy here restores what you paid rather than compensating you for a broader loss, and it applies even though the thing itself is completely gone and cannot simply be handed back and exchanged for a similar replacement.
What you need to show for even this narrower remedy
To recover the price, interest, and expenses under this rule, you still need to establish that the defect was hidden rather than something an ordinary inspection would have revealed, and that the defect actually caused the loss of the thing rather than some unrelated event. If the seller disputes being unaware of the fault, that dispute affects which branch of this article applies — the narrower remedy described here, or the fuller one that applies when the seller knew.
What this provision does not cover
This rule addresses loss caused specifically by the hidden defect itself. It does not extend to a loss you caused yourself through mishandling, nor to ordinary deterioration unrelated to the fault, nor to expenses beyond those actually tied to the contract of sale. Where the cause of loss lies outside the hidden defect, this particular remedy does not apply, and whatever other rules govern that separate cause take over instead.