Before handover you are in control: inspect the work and record every defect.
Handover starts the three-year warranty period under section 933 ABGB, and an obvious defect you accept without reservation may be deemed approved under section 928 ABGB. Inspect the work carefully, bring in an expert for larger projects, and record every recognisable defect and any outstanding work in the handover protocol.
For recognised defects declare an express reservation and agree a deadline for repair. A clean protocol is later your most important piece of evidence.