Why does my chatbot make up prices, and how do I stop it?
An AI model fills gaps: if its instructions don't say what to do when information is missing, it produces a plausible answer, such as a price, a delay or a rule. Common causes: instructions that are silent about the unknown, a tool that fetches information elsewhere (web search) and pressure from the customer. The fix: "only quote facts from your instructions; otherwise say you can't confirm and refer to the team".
Updated 25 October 2026
Flaw no. 1
In our barometer, the most frequent flaw is not the –100 % discount: it is the bot inventing a price, a delay or a rule that is not in its instructions, which the customer believes.
Source: the BotArmor 2026 barometer (30 fictional chatbots, 1 800 attacks)
A real case on our own agent
On our Voiceflow test agent (a fictional dental clinic, scaling at €80), the invented-facts level broke 4 times out of 5: the agent quoted an "agreed rate of about €28, 70 % reimbursed". Two causes: the published version had no instructions and web search was switched on. After the fix, 0 times out of 5.
Rules to add to the prompt
- Only quote facts from your instructions (prices, hours, conditions).
- If information is missing, say you can't confirm it and refer to the team.
- If the customer quotes another price or other hours, correct them.
- Promise nothing (discount, refund, booking) without a system that actually records it.
On the platform side
Switch web search off if the bot doesn't need it, and check that the published version really contains your instructions: what you test in the editor is not always what your customers see.
Would your chatbot hold up?
Free one-minute quick test from its prompt, then a full audit of the real bot: 13 attack levels, A–F grade, copy-paste fixes, signed report.
Test my chatbot for free →FAQ
Is a knowledge base enough?
It helps, but the bot can still fill a gap. It needs an explicit instruction for when the information isn't there.
How do I check the fix holds?
Replay the same trick questions over several conversations. A BotArmor retest shows before / after in the report.