its quite common not to replace or check cables, if if the quote says they will they don't because the bloke doing it doesnt have the time.
the cables wil look "tarnished" due to sunlight and age, but thatdoesnt mean they are no good.
The problem is as i said galaxy's monitor the resistance which includes the cables, if when it was origonaly installed some one made joints and did not solder them (quite common) these joints can go high resistance, galaxys have a 1k end of line resistor (and a 1k shunt) if the joint changes by 200 ohms its too much, the 9100 wouldnt worry about it.
i have seen cables that have their outer sheeth removed so they are less obtrusive this is no use since these can also cause short ccts.
My mate who is an alarm engineer used to work for a company where they would insist on one cable for one device, no matter what that device is (i.e no joints allowed)
its amazing some of the "horror storeies" he tells me, he has seen more than me.
I guess it comes down to cost. being the reasons they dont change the cables, which is why i suggest you ask for a brand new alarm (which includes cabling)
ocasionaly there are places that have 2 alarms one works the other doesnt, but the working one has all new cables and the old one is just left there.
and dont let anyone tell you a wireless alarm is good