Foundation repair does not have to hurt a sale. What hurts a sale is a repair nobody can evidence.
The folder a buyer wants
The structural engineer's original report — the diagnosis and the specified scope.
The contractor's scope and contract, showing what was agreed.
The pier-by-pier record — position, depth, refusal pressure or torque.
Photographs of brackets before backfill.
Pre- and post-work floor elevations.
The engineer's verification letter, where one was obtained after completion.
The warranty document, with the transfer terms.
Assembled, that set turns "the house had foundation work" into "the house had a documented, engineered repair". Those are very different conversations.
Transferability is the line that matters
Most contractor warranties are described as lifetime. The question a buyer asks is whether it transfers.
Common arrangements: transferable once, transferable for a fee, transferable within a time limit, or not transferable at all.
Find out before the repair rather than at the sale, because it is a term that can sometimes be negotiated at the time of purchase and never afterwards.
Also check what survives if the contractor ceases trading. Some warranties are backed by a third party; many are not, and a warranty from a company that no longer exists is a piece of paper.
Disclosure
Requirements vary by jurisdiction, and the safe assumption is that known foundation repair is material and must be disclosed.
Attempting to conceal it is both a legal exposure and, practically, unlikely to work — piers are visible to any competent inspector, and the excavation and patching leave traces.
Disclosing with the full folder is a much stronger position than disclosing without it.
What a buyer's inspector will do
Look for evidence of piers, look at cracking, check floor levels, and read whatever documentation is offered.
If the documentation is complete, the conversation is usually short. If it is absent, the inspector will recommend a structural engineer, and the buyer will either walk or ask for a price reduction sized by uncertainty rather than by the actual risk.
Repair before listing, or price for it
The two viable strategies.
Repair and document, which removes the uncertainty and lets the house be priced normally. This works best where the repair is straightforward and the documentation will be good.
Disclose and price it in, providing the engineer's report and quotes so the buyer knows the number rather than imagining one. Buyers discount unknown risks far more heavily than known costs.
The strategy that fails is repairing without documenting, which incurs the cost and keeps the uncertainty.
Where the value actually is
An engineer's verification letter after completion is inexpensive and it is the single most persuasive document in the folder, because it is the only one written by someone with no financial interest in the outcome.
Getting it costs a small fraction of the repair and it is easiest to arrange while the engineer is already involved. Years later, at sale, it is difficult or impossible.
Buying a house that has had work
The same folder, read from the other side. Ask for all seven documents. Where they exist and the work was engineered, a repaired foundation is arguably better than an unrepaired one of unknown condition.
Where they do not exist, budget for your own engineer's assessment before removing the contingency. A visual inspection cannot tell you what the piers reached, and that is the thing that decides whether the repair was worth what was paid.
Timing the repair against the sale
Repair work leaves a disturbed perimeter and fresh landscaping, which is visible and invites questions. Doing the work several months before listing lets the ground settle and the planting recover.
It also gives time for the post-repair elevation readings to be repeated once, which demonstrates that the house is now stable rather than merely repaired — and that is a stronger claim than any warranty.