Can I ask for a second opinion on a repair charge without accusing the contractor of dishonesty?

With the bathroom floor lifted, the contractor sent a photograph and said, "The subfloor needs replacing. That's another $1,800 if you want us to keep moving." My partner replied yes. I asked for the extra work and price in writing before we agreed.

Our US home repair contract is for $12,000 and says unforeseen additional work needs written approval. The photo shows a damaged-looking patch, but neither of us is qualified to say what needs replacing or how far it extends. The contractor says the bathroom will remain unusable while we decide, and we are sharing a small downstairs washroom with two children.

I understand why my partner wants progress. I also know that "replace subfloor" doesn't tell me the area, materials or labour being added. The [FTC's contractor guidance](https://consumer.ftc.gov/articles/how-avoid-home-improvement-scam) recommends written estimates describing scope, price and dates. I want that clarity here; I haven't decided the problem is invented.

How do we get a properly explained change and, if needed, an independent assessment without creating unnecessary delay? I don't want the cost of an unusable bathroom to make us approve an amount we still cannot describe.