Firstly, I am not an engineer, however the concepts involved are not that difficult to grasp. Underpinning is simply one way to stabilise the movement of house wall but is not the answer in all cases. Digging out and introducing a new stabilised footing under you house slab can and will rectify a lot of the issues, but is this expensive repair technique really the only answer?  The other alternative is using an expensive resin injection system to push up the sinking slab to rectify the cracking walls.
All concrete slabs and footings are engineered to be serviceable for the life of the house, however the engineers do request that the entire perimeter of the house be surrounded by pathways that direct water away from the slab edge. When looking at houses for sale, quite often this has been neglected.
Understanding that cracks in ceilings or walls are due to slab heave, that occurs when the soil moisture content under the house has been changed and is no longer uniform under the slab. Reactive clay soils will swell when damp and shrink when dry. When the soil around the outside of the house becomes wet the clay soils absorb moisture and expand pushing up on the external edges of the slab or strip footing. The soil in the middle of the slab remains constant, so the expansion of the slab and cracking of the walls begin. These expansive forces are powerful enough to lift a house and easily crack the concrete strip footings of older homes.
If for example you do spend many thousands of dollars with either resin injection or underpinning, but do not rectify what caused the issues, you may soon find out that any warranty provided by the companies involved is probably void.
In lots of cases simply doing what was requested by the original engineer, making sure that water is directed away from the house and that the house has a decent pathway surrounding the slab to prevent heave is all that may be required.
I would suggest simply doing this and observing the cracking is a great start, then if the ground is not more stable after a year or so, then consider spending your money with an established underpinning or resin injecting business. You may only require patience, some quality crack filler and a slap of paint to keep it looking good.

When you're at an open inspection looking at a house, you get to see all the nicely decorated rooms and freshly painted walls. But what is through that personal access hatch that you need to know about?

​This space located between the ceilings that you can see and under the roofing surface that you can see from the road, is full of expensive repairs that let's face it, do not get repaired before a sale as they are not seen. This area is often only rectified, if the house has been on the market so long that it has had multiple prior inspections and it becomes apparent to the seller that it will not sell unless, at an auction where no inspection was arranged by the purchaser. The Vendor may at this point decide that they desperately want to sell and will spend some money to patch it up for sale, or spend so much rectifying the issue, they end up keeping the property after doing the renovations.
The issues can be simple insulation installation issues that may cause ceiling fires or even ceiling collapse. Older houses often have halogen downlights, that require 200mm clearance from the recessed luminaire, 200mm clearance from a timber structural member and 50mm clearance from the transformer. This is often not done and a fire can occur. 
Other insulation issues are missing insulation batts, that will result in insufficient thermal areas, but this is a minor issue compared to a collapsed ceiling. Where no insulation is present in a ceiling, the unpainted side of the exposed gyprock absorbs moisture, gains weight and sags. The sagging gyprock then pulls through the nails and glue that holds the ceilings up. From inside the room all you may notice is a small ring crack around the nail or screw head. Each room that requires the ceilings to be replaced however can cost up to $3,000 to remove, replace and repaint. The costs are so high that an electrician will need to be involved, the insulation will probably require replacement and the clean up required afterwards. 
Damaged timberwork can be the result of prior tradesmen simply removing structural timbers or altering truss sections to make their job easier. Other notable areas of damage is truss plate delamination, mould damaged timbers, chemical delignification damage, wood rot or termite damaged timbers. All of these items are an expensive repair and can require engineering recommendations and certification. The structural members of a roof are designed by an engineer and can not just be modified or repaired on site by anyone. Roof sheeting can rust and lead flashings can crack allowing for moisture ingress to the ceiling space, also roof tiling can crack or terracotta roof tiles can fret.