AI Guides › Money & Business
Using AI To Sanity-Check A Big Purchase Decision
By Nigel Guy · 2 min read
Facing a big purchase — equipment, property, a major contract — the common
move is to ask AI to help justify the decision you're already leaning
toward. You feed it the reasons you already believe, and it hands back a
polished version of your own case. That's agreement, not a check.
The rule: AI is far more useful as a devil's advocate on a big purchase
than as a cheerleader — ask it explicitly to argue against the decision
you're leaning toward, using only the numbers and constraints you give it.
The mechanism: the devil's advocate prompt
- Write out the decision and your reasoning honestly, as if you had to
defend it to a genuinely sceptical friend, not a supportive one.
- Ask AI to take the opposing position explicitly — the strongest
reasons this could be a mistake, using only the facts you've provided,
not inventing new ones it can't verify.
- Answer each objection honestly. Can you answer it with actual
evidence, or are you hand-waving past it because you've already decided?
- Ask it to identify the single assumption your case leans on hardest,
and check whether you've actually verified that assumption or simply
believe it.
- Make the decision with the objections sitting on the table, rather
than deciding first and hunting for reasons afterward.
What to skip
Skip asking an open-ended "should I buy this" and taking whatever comes back
as a verdict — that produces a plausible-sounding answer either way,
disconnected from your actual situation. Skip treating this as a substitute
for real financial diligence — getting actual quotes, checking your actual
cash flow. This is a thinking tool, not a research tool. And skip running
this exercise after you've already signed anything; the whole value is in
surfacing objections while you can still act on them.
Guardrails
- The objections it raises are only as good as the information you gave it —
it can't verify actual market prices or your actual finances, so check
those separately.
- It can generate objections that sound serious without being specific to
your situation — weigh each one honestly rather than treating volume of
objections as a verdict in itself.
- A decision with major consequences deserves a second human opinion too,
not AI alone standing in for one.
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