I can provide general guidance, but here are key considerations:

**Potential Concerns:**

- **Tax implications**: Below-market rent may affect depreciation deductions and could trigger IRS scrutiny
- **Legal liability**: Family arrangements can become complicated if disputes arise; you may lose landlord protections
- **Financial impact**: Reduced cash flow affects your retirement income needs
- **Future complications**: If you need to sell or refinance, lenders may question the arrangement
- **Family conflict**: Money and housing can strain relationships if terms aren't crystal clear

**Possible Mitigation:**

- Document everything with a written lease, even for family
- Charge fair market rent AND gift/loan him the difference if desired (cleaner tax treatment)
- Consult a CPA about rental property deduction implications
- Consider your actual retirement cash flow requirements
- Discuss exit strategies (what if circumstances change?)

**Alternative approach:**
A fair market rent arrangement with separate financial help (direct gifts, loans, or co-signed assistance elsewhere) is cleaner than below-market rent on the property.

**Bottom line**: It's not inherently bad, but treating it as a business arrangement with proper documentation protects both you and your son while keeping your retirement income stable.

I'd recommend consulting a tax professional and attorney before formalizing anything.