Ordering your own independent appraisal before wiring money is reasonable due diligence, and any operator worth working with will understand that. It does not automatically get you walked off a deal. An operator who reacts badly to the request is telling you something important.
A few things to understand first. In a BRRRR deal (Buy, Rehab, Rent, Refinance, Repeat), the refi appraisal is the number that determines how much money you can pull out after the property is fixed up. If that number is wrong, the whole return model falls apart. Your operator's projection is an estimate of what an appraiser will say after the work is done. That is not the same as an actual appraisal.
The problem with 18-month-old comps is real. In a lot of markets, values have moved enough in that window to change the math materially. A comparable property, a "comp," is a recently sold similar home used to estimate what yours is worth. The further back those comps are, the less reliable the projection.
What you can do right now, before funding, is hire a licensed appraiser to give you an "as-complete" or "ARV" (after-repair value) appraisal. This is a professional opinion of what the property will be worth after rehab. It costs a few hundred dollars and gives you an independent data point. You can also pull recent sales yourself on Zillow or Redfin and see whether the operator's comps hold up.
One thing worth knowing: operator due diligence, meaning how you evaluate the person running the deal, matters just as much as the property math. The strategy guide for JV capital provision covers this directly. Your outcome depends heavily on who you are partnering with, not just the numbers they show you.
A licensed appraiser is the right professional for the valuation question. For anything about the legal structure of the partnership itself, that needs a real estate attorney.
What market is the deal in, and do you have access to the comp addresses the operator cited?
