As above, the norm would be to make sure the cables meter out, there's nothing obvious maybe lift a couple of carpets near the door jambs to check for damaged, poorly run cables.
Once you are happy, make the customer aware they are paying a lot less by you utilising existing cabling and document it and the fact it's not covered under any warranty, on your spec refer to each device as 'utilising existing cabling' too, this is the norm in this type of scenario.