Short answer: Check for damp, cracks, stains, maintenance. Ask about insulation, heating, roof. Do not reveal budget to agent.
Look for damp smells, cracks in walls, water stains, and poor maintenance. Ask about insulation, heating, and when the roof was last done. Check the neighbourhood at different times of day. Take photos and notes. Do not reveal your maximum budget to the agent. Everything you say to the agent can be used in negotiation.
Red Flags: Musty smell = possible leak,Cracks above doors = foundation issues,Single glazing = cold, expensive heating
Questions: When was roof last replaced?,Is insulation in walls and ceiling?,Any previous leaks or flooding?