Read the water heater label
Find the tank and read the manufacture date. Past ~12 years, a water heater can leak any day. Look for rust at the base.
Open the electrical panel door
Check the brand — Federal Pacific, Stab-Lok, or Zinsco are worth flagging — and note the service size on the main breaker.
Glance at the pipes and outlets
Grey plastic pipe may be poly-B. Two-prong outlets mean no ground; kitchens and baths should have GFCI test/reset buttons.
Walk the outside
Watch which way the ground slopes — toward the house is a drainage problem — and eyeball the roof for curling shingles or moss.
Bring a fridge magnet
It sticks to galvanized steel but not lead — a two-second test on the service line and supply pipes.