1. Ask about a very specific fact (a small company's founding year, a rule number). Then ask: 'How confident are you? What source would confirm this?'
2. Repeat with: 'If you are not sure, say you don't know.'
3. Give the source text yourself and ask: 'Answer only from the text below. If the answer isn't in it, say so.'
4. Ask for references, then check two of them actually exist.