How can you possibly tell if copper wiring needs to be replaced without being able to see it and not performing testing on it? Makes no sense.
Why limit this to copper?
No you can't tell without seeing it, that should be obvious and I don't think anyone has suggested that you can make any assessment without seeing the installation.
My point is that you can often tell if a full rewire is required based on an inspection alone.
I'll take a domestic installation as an example.
The customer wants your opinion on the installation and a quote to change a couple of rooms to downlights, add extra sockets in every room because there's only 1 in each room, replace all switches/sockets with some trendy shiny metal.
You unscrew a few pendant caps and find imperial twin with no CPC.
The CU is a wooden backed wylex, a little bit loose on the wall as the wooden wall plugs have shrunk over the years. 5 circuits, cooker, ring, immersion heater, lights up, lights down.
There's 1 ivory single socket in every room with plate screws top and bottom.
Bonding is a rather skinny bare tinned conductor half-arse wrapped around a water pipe.
The immersion heater circuit has been attacked by a plumber to feed a shower pump and a replacement boiler.
The attached garage has all the typical DIY additions with round joint boxes and dangly cables.
There's probably even a greenhouse somewhere with a plastic twin socket on the wrong pattress and a rusty old tubular heater.
I'd go out on a limb and say that it's probably going to be better to rewire it than try to bring it up to current standards.
The lighting needs a cpc added to all points so you may as well rewire it as mess around trying to add a CPC.
The ring really needs splitting in to two circuits and by the time you've done that and extended to to all the new points there'll be so little of the original installation left that you might as well have rewired (plus it would be cheaper and quicker)