Concrete work is usually undertaken in changing conditions. External factors such as the weather plays a critical part in carrying out the work.
Furthermore, ground conditions vary and is not constant from area to area. A concrete foundation needs to be adjusted in order to take into account whether the ground contain rock, buried rubbish or tree roots. The consistency of the ground also needs to be taken into account, e.g. whether the ground consists mainly of sand or clay. Ground conditions will have a direct impact on the quoted price as it will be extremely difficult to quote a set price without taking the subsequent conditions into consideration.
Concrete can show signs of cracks over an extended time period. Little to nothing can be done to avoid such a scenario, expect for ongoing maintenance and remedial work. Due to the nature of concrete, this is likely to end up in a debate between the contracting parties where the cost of maintenance and aesthetics of the surface will be queried.