Calling the AI bluff: Adding "Do not guess" cut made-up fields from 71% to 20%

A test of web extraction services found that adding the instruction "Do not guess" dramatically reduced the rate at which AI models invented missing data fields from 70.7% to 20.2%. The study tested 16 AI models and paid APIs across 42 page pairs, revealing that even with the instruction, most models still fabricated answers when fields were absent from web pages, with Gemini 3.8 Flash performing best at only 2.8% made-up fields.