If in doubt
Definition 1 of 1
Pro Tip 1/3Precautionary Advice
Use 'if in doubt' to advise caution when someone is unsure, suggesting they seek clarification or take careful action. 
If in doubt about the expiration date, better not consume the product.
Pro Tip 2/3Non-specific Situations
'If in doubt' applies broadly and can be used for many uncertain situations, not just specific problems. 
If in doubt about your route, always have a map ready.
Pro Tip 3/3Decision-Making
Highlighting indecision, 'if in doubt' is often used before making a choice or when advising others to be sure. 
If in doubt, always pick the safer option.