If it was me I would offer free electrical tests and then tell them about my (fingers crossed) bad findings. Id also maybe mention about current electrical regulations (17th edition boards, bonding conductor size etc) and possibly drop in that instead of it taking 5 seconds for you to stop being electrocuted if there was a fault and something had became live it would only take 0.2. I would probably show them what a new board looked like and then leave it with them
note: I was told 5 seconds. I haven't looked it yet up so this could be bad advise and require consideration and a bit of stick for me, but if not pretty a pretty effective point and I would of never forgot something.
Incase anyone thinks I mean leave the actual board with them I mean the thought