For anything into five figures, hire an independent structural engineer first. They diagnose and specify without selling the repair, and their report becomes the common specification every contractor bids against.
More detail
The structural difference between the two evaluations is not expertise, it is incentive. A repair contractor evaluates for free and produces a proposal for work they will perform. Many are technically excellent and diagnose accurately. The structural issue is that the person defining the scope also benefits from the scope, and on a job where the number of piers is a judgment call, that is worth naming plainly. An independent structural or geotechnical engineer charges a fee, typically a few hundred to around a thousand dollars for a residential evaluation, and produces a report: what is happening, why, what the repair needs to accomplish, and often a specified design with capacity and placement. They do not perform the work. What that fee buys. A diagnosis with nothing riding on the outcome, including the possibility that the answer is monitoring rather than repair, which no contractor will ever conclude. A common specification, so multiple bids are priced against identical scope and the comparison becomes meaningful. A document for the file that supports resale disclosure and reassures a future buyer. And leverage, because a contractor bidding against an engineered spec is bidding on execution rather than on scope. When it is not necessary. A single weeping vertical crack in a poured wall, a straightforward crawl space post replacement, or any repair in the low four figures where the diagnosis is not in dispute. When it is close to essential. Bowing walls, differential settlement, anything where two contractors have proposed different repair families, and anything where the recommendation is into five figures. Ask for someone who does residential foundations specifically, and confirm they do not have a referral relationship with a repair company.