Check the repairs are decent and check out repairer has good feedback or VOSA/insurer approved certs. These badly damaged cars can be 'fixed' by back street garages and may look nice and shiny on the surface, but if anything related to the chassis hasn't been done properly you can have issues with handling, braking, other components suffering, abnormal tyre wear. Fire/water damaged may sound ok as a damage, physically the car should be ok, but you can get some nasty electrical gremlins.
See if you can find out what the damage was.
Also check out insurance, some insurers won't touch CAT D/C repaired vehicles.