Especially in older homes, I write on the contract or invoice that I recommend checking all wiring and that I am not responsible for any existing wiring or connections to existing wiring. If the wiring really should be replaced I will write that. Don't know if this covers me but it might help in court. I think this is a big problem. If you're unlicensed and uninsured you have no worries. The owner assumes responsibility since they hired someone without a license.
