Claude stated unverified factual claim without checking — reported wrong agency directory status

Summary

During an AI chatbot visibility audit session, Claude stated in a client report that agency Effectix was not listed on webtop100.cz — without actually verifying this claim. The statement was presented as a factual finding and included as an action item in both the Markdown report and the generated PDF.

When the user questioned the claim, Claude then fetched the page and discovered that Effectix is listed on webtop100.cz (at /agentury/effectix-com), including with awards (2023 #1 in AI category, multiple #1 in Performance Campaign).

What happened

1. Claude inferred the claim from ChatGPT probe responses — ChatGPT cited webtop100.cz for competitors Taste and Fragile, but not for Effectix.
2. Claude incorrectly concluded "Effectix is not on webtop100.cz" from this indirect signal, without fetching the page to verify.
3. The false claim was written into a client-facing PDF report as an action item ("Add Effectix to webtop100.cz").
4. The user had to explicitly ask "are you sure about this?" before Claude checked.

Root cause

Claude made an inference from absence of citation (ChatGPT didn't cite webtop100 for Effectix) and stated it as a verified fact (Effectix is not on webtop100). No WebFetch or search was performed to verify the claim before writing it into the report.

Expected behavior

Before asserting a factual claim about whether a brand/entity exists or is listed somewhere (especially in a client deliverable), Claude should verify the claim directly — either via WebFetch, search, or at minimum flag it as unverified. The pattern "I didn't see X cited, therefore X doesn't exist" is a logical error that should trigger a verification step.

Suggested improvement

For research/audit tasks that produce client reports: Claude should treat any "X is not present/listed" claims as requiring direct verification before inclusion, not inference from indirect signals. A simple note like "(not verified — inferred from probe data)" would at minimum flag uncertainty to the user.

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Reported by user after noticing the error in a generated PDF report. Claude corrected the report after verification but only when prompted.