An Ontario PI is hired to investigate infidelity. The client asks the PI to install listening devices in their spouse's vehicle without the spouse's knowledge. What should the PI's response be?

1. Proceed with caution, as it is a grey area in the law.
2. Only install it if the client provides written consent.
3. Install it but ensure the recordings are only used for the client, not in court.
4. Refuse the request, as installing listening devices without consent is generally illegal under Canadian law (e.g., criminal code interception of private communications).