Before agreeing a fee, ask the reviewer to test the basics: whether the applicant can qualify for lawful permanent residence, whether anything in their history raises admissibility concerns, and whether an EB-1 or EB-2 determination is realistic given visa availability. Paying the processing fee does not remove those requirements, and no adviser can waive them.
Get the hard questions asked early
A scoping conversation is worth more when it starts with what could go wrong. Ask which facts the reviewer considers unresolved, what evidence would resolve them, and what would make the reviewer advise against applying at all. Record the answers.
If a professional will not identify any risk, that is information about the professional. The program requires eligibility, admissibility and an available visa; a scope built around only paperwork assembly leaves the decisive questions to nobody. It is worth asking those questions in a particular order, because only one of them is about money.
First, does the applicant independently qualify for lawful permanent residence through an EB-1 or EB-2 determination, which turns on that person's own record rather than on any payment. Second, is the applicant admissible, decided on its own facts. Third, is a visa available in the relevant category.
A reviewer who reaches a provisional view on the first two from documents the household already holds has delivered the whole value of an early engagement, and has done so before the nonrefundable processing fee is spent.