skm1981, good evening.
In a lot of cases a wall crack internally or externally is not by definition Subsidence, experience will assist greatly, but is fallible.
A crack following the line of a Chimney Flue in a Sandstone property is probably Sulphate attack.
Internally cracks in straight lines on [especially] ceilings are probably down to Plasterboard sheets.
Testing for Subsidence, there are several ways to find the geology of the ground under the property, one fast way is the App for the I=Pad from the BGS.
If as happens up here a lot the property may be sited in an area of Old mines, Leaking drains are a killer but silent.
When an Insurance claim for Subs comes in it is a process of elimination if you want to be sure as to what you are dealing with.
1/. Instruct a CCTV survey of all the drains within a 10 / 15.m radius of the subs area.
2/. Monitor, some people like to use studs stuck on to the wall and take measurements over a 6 month period, this to eliminate the cold and warm months thus eliminating thermal Movement
3/. The Acid Test?? instruct a "Level Monitor" survey, this takes the form of permanent studs fixed to the wall over the area of concern, take readings over the same time scale as above. I say "Acid Test" because, the definition of Subs in insurance terms is the vertical downward movement of the foundations,
OK the above is the basics, but will give a good idea of what is going on as far as Subs investigations are concerned.
As for excavations? OK But difficult to absolutely confirm with no creditable evidence ?
Ken.