"It looked like concrete. It wasn't."
Sha Tin private estate, customer was sure her bedroom wall was solid. The rebar detector said otherwise — drywall over plaster, no structural backing. We stopped, called the customer, explained the risk, and offered two paths: switch to a load-bearing wall on the other side, or add a 6 mm steel reinforcement plate. She chose the steel plate. Adds HKD 3,200 + a half-day delay; bed has held for 14 months without a creak.