Run a vendor compare that cannot outrank the source page

Two suppliers, one renewal date, and a chat that already sounds sure. The price in the brief is not on either website. You almost forwarded it.

The short answer

The sequence below is the control path: same vendor pages, same prompts, product names kept exact.

Use the tool to structure three options, mark unknowns [NEED], and argue against the leader. Then open every price and feature on the vendor's own page before you decide. ChatGPT, Claude, and Gemini can all hold that brief. None of them is the purchase order.

Why the brief sounds finished

A comparison with no sources still has sentences. The model would rather complete the table than leave a cell blank. Your job is the blank cell. A decision you can make in one sitting beats a week of tabs. The longer method for hire-versus-tool choices is decision briefs.

The 45-minute compare

1. Write the decision in one line. Keep the current vendor, or trial the alternative.
2. List hard constraints: delivery, must-have features, a budget you label as your estimate.
3. Provide only facts you gathered from each vendor's current site or quote. Note the date you checked.
4. Prompt: "Build a decision brief: three options max, criteria, risks, unknowns as [NEED], a recommend-or-kill line. Do not invent facts."
5. Prompt: "Argue against the leading option in five bullets."
6. Open every number and feature on the vendor's page or the signed quote.
7. Decide in the same sitting, or put the decision on the calendar within 48 hours.

Stress tests worth keeping: "What would make the recommended option fail in our busy season?" "Which constraints did I state that you ignored?" "List claims in your brief that are not in my facts, and rewrite them as [NEED]."

ChatGPT

ChatGPT is useful when web research is on and you want candidate sources gathered into the brief. A snippet is not the page. Open it. Connected apps do not make a vendor's pricing page authoritative. The date you checked still matters.

Claude

Claude is useful for the criteria, the failure modes, and the argument against the leader. If the plan includes a research mode, you still open the cited pages. Live promotional prices, contract fine print, and regulated advice (legal, clinical, tax) are weak spots. "Who is best" with no criteria is not a decision.

Gemini

The Gemini Apps Privacy Hub says some responses are grounded on Search. It does not say every answer used Search, and it does not say a grounded sentence is true. Sources in Gemini Apps show up when Gemini provides links. If there is no Sources button, that reply had no links.

Inside Workspace, sources help says web search stays off unless you turn it on, and that Gemini can miss a source, cite the wrong file, or present a source it made up. If the opened page does not show the price, you do not have the price.

Which to pick when

• You want a fast pile of candidate links, then you will open them → ChatGPT with research on
• You want the counter-argument and a tight brief from facts you already provided → Claude
• The quotes and the spec already sit in Drive or Gmail → Gemini on the work account, with web search only if you turned it on and you still open every link
• The decision is a contract, a clinical claim, or a tax position → the brief can list questions. A qualified person answers them.

Close the brief

• Recommended option:
• Why, in two sentences:
• First action within 48 hours:
• What would make you stop:
• Decision date:

Save the brief with the outcome and the date. Next quarter you will see whether the call held.

Example (illustrative): a pest-control supply renewal

Problem: the chat named a price the supplier's page did not show. What was built: the price rewritten as [NEED], then filled from the quote PDF dated that morning. Tools it lives in: one brief in the tool the owner already had open. Owner still does: the decision. Payoff: not measured.

Mistakes and limits

• Seven options. Three is the cap.
• A price with no date and no URL.
• Treating a Sources chip as verification.
• Mixing "research more" with "decide today" so neither happens.
• Asking for regulated advice and forwarding the paragraph.

Doing this inside the tools you already use

If you would rather have this exact job drafted from the software you already use, with you still approving every send, see how a custom build works.

FAQ

Can I skip opening the links if Sources is showing?

No. Google's own Workspace help says a cited source can be the wrong file or a source the model made up. Open the page.

How many vendors belong in one brief?

Three. More than three is usually a way to delay the decision.

What if the pages disagree with the quote in my inbox?

The quote you were sent, dated, wins over a marketing page, and both win over the chat. If they disagree with each other, that disagreement is a [NEED] you ask the vendor about. It is not a cell for the model to average.

Is web search on inside Workspace Gemini?

Workspace help says web search stays off unless you turn it on. Check the setting on the account you are using before you assume the brief looked at the web.

Keep these

• Three options, constraints you actually have, [NEED] for the rest.
• A pass that argues against the leader.
• Every price opened on the vendor's page or the quote, with the date.
• A decision date on the calendar.

Sources

• Gemini Apps Privacy Hub
• Sources in Gemini Apps
• Workspace sources
• Anthropic: reduce hallucinations

Related reading

• Hire or buy a tool, decided in one sitting
• Pick ChatGPT, Claude, or Gemini for the job
• Stop invented facts before they reach a customer