Ask what they do in the first month, before touching a single application. If the answer is "we start the essay," that's your red flag.
A good consultant spends the early weeks understanding your child, not producing a document. That means real conversations about what your child actually cares about, what they're good at when no one's grading them, and what kind of environment they'd thrive in. If none of that comes up before the essay does, the process is backwards.
Second thing to check: do they talk about "getting in" or do they talk about "fit"? Consultants chasing a brand-name outcome will push your child toward whatever profile is trending that admissions cycle. The ones doing this well are looking for the handful of schools where your child would actually be happy and would actually get in, and they're honest when those two lists don't fully overlap.
Third, ask how much of the essay your child will actually write. If a consultant is vague about this, or proud of how "polished" their essays turn out, be careful. Admissions officers read thousands of these. They can tell when a seventeen-year-old didn't write their own sentences, and so can I, honestly, within a paragraph or two.
Last thing. Watch how they talk to your child directly, not just to you. If most of the planning conversation happens between the consultant and the parent, with the student mostly nodding along, that's usually a sign the process is being done to the child rather than with them.